Method of cooling series-connected heat sink modules

ABSTRACT

A method of cooling two or more heat-providing surfaces using a cooling apparatus having two or more fluidly connected heat sink modules in a series configuration can include providing a flow of single-phase liquid coolant to a first heat sink module mounted on a first heat-providing surface. The method can include projecting the flow of single-phase liquid coolant against the first heat-providing surface within the first heat sink module and causing phase change of a first portion of the liquid coolant and thereby forming two-phase bubbly flow with a first quality. The method can include transporting the two-phase bubbly flow to a second heat sink module and projecting the two-phase bubbly flow against a second heat-providing surface within the second heat sink module and causing phase change of a second portion of the coolant and formation of two-phase bubbly flow with a second quality greater than the first quality.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 13/169,355 filed Jun. 27, 2011; U.S. patent application Ser.No. 13/169,377 filed Jun. 27, 2011; and U.S. patent application Ser. No.14/604,727 filed Jan. 25, 2015 and claims the benefit of U.S.Provisional Patent Application No. 62/069,301 filed Oct. 27, 2014; U.S.Provisional Patent Application No. 62/072,421 filed Oct. 29, 2014; andU.S. Provisional Patent Application No. 62/099,200 filed Jan. 1, 2015,each of which is hereby incorporated by reference in its entirety as iffully set forth in this description.

FIELD

This disclosure relates to methods, apparatuses, and assemblies forcooling one or more heat sources, such as one or more heat sourcesassociated with an electrical, mechanical, chemical, orelectromechanical device or process.

BACKGROUND

Maintaining electronic devices, such as microprocessors in servers,within safe operating temperature ranges is a challenging problem thatis only increasing in importance and difficulty as semiconductortechnology continues to progress and as popularity of cloud storagecontinues to grow. State of the art microprocessors can easily producemore than 40 thermal watts per square centimeter, and power electronicscan produce heat densities three times higher.

There is a need to cool these devices efficiently. According to theDepartment of Energy, nearly three percent of electricity used in theUnited States is devoted to powering data centers and computerfacilities. Approximately half of this electricity goes toward powerconditioning and cooling. Increasing the efficiency of cooling systemswould lead to dramatic savings in energy nationwide. More efficientcooling is also needed in transportation systems due to the rapidlyincreasing adoption of hybrid and electric vehicles that rely on complexelectrical systems, including electric motors and batteries that producesignificant amounts of heat. More efficient cooling of these electronicsystems would translate to increased driving range and utility of thevehicles.

The majority of computer systems in residential and commercial settingsare cooled using forced air cooling systems in which room air is forced,by one or more fans, over finned heat sinks mounted on microprocessors,power supplies, or other electronic devices. Each heat sink adds massand cost to the computer and places mechanical stress on the electronicdevice to which it is mounted. If the server is subject to vibration,such as vibration caused by a fan, a heat sink mounted on top of amicroprocessor can oscillate in response to the vibration and canfatigue the electrical connections that attach the microprocessor to themotherboard of the computer.

Another downside of air cooling systems is that cooling fans commonlyoperate at high speeds and can be quite noisy. As air passes overelectronic devices, the air, which is at a lower temperature than thesurfaces of the electronic devices, absorbs heat from the electronicdevices, thereby cooling the devices. These air cooling systems areinherently limited in terms of performance and efficiency due to the lowvolumetric heat capacity of air, which is much lower than the volumetricheat capacity of water and other coolants. Because air has such a lowheat capacity, high flow rates are required to ensure adequate coolingof even relatively small heat loads. For instance, a flow rate of about5 to 10 cubic feet per minute (cfm) of air is needed to cool a 100-wattheat load. For heat sources such as microprocessors, which as mentionedabove can easily produce more than 40 watts per square centimeter, veryhigh volumetric flow rates are required to prevent overheating. For aninstallation of one rack of servers, which is commonly used in computerrooms of small businesses and schools, two air conditioning units sizedfor a typical U.S. home are required to cool the computer room. Typicaldata centers, which can have several hundred racks of servers, must beequipped with special computer room air conditioning (“CRAC”) units thatare large and expensive and must be professionally installed, oftenrequiring substantial modifications to the facility to accommodate theCRAC, including installation of structural supports and custom airducting.

Many electronic devices operate less efficiently as their temperatureincreases. As one example, a typical microprocessor operates lessefficiently as its junction temperature increases. FIG. 64 shows a plotof CPU power consumption in watts versus junction temperature. Thebottom curve shows static power consumption of the microprocessor andthe top curves show total power consumption for switching speeds of 1.6GHz and 2.4 GHz, respectively. Total power consumption includes bothstatic power consumption and dynamic power consumption, which varieswith switching frequency. As shown in FIG. 64, as the temperature of themicroprocessor increases, it consumes more power to provide the sameperformance. In air cooling systems, it is common for fully utilizedmicroprocessors to operate at or near their maximum rated temperature,resulting in poor operating efficiency. In the example shown in FIG. 64,the microprocessor uses over 35% more power when operating at 95 degreesC. than when operating at 45 degrees C. To conserve energy, it istherefore desirable to provide a cooling system that will allow themicroprocessor to operate consistently at lower temperatures.

Operating speeds of next generation microprocessors will continue toincrease, as will heat fluxes, where heat flux is defined as heat loadper unit area. Conventional air cooling systems will soon be incapableof efficiently and effectively cooling these next generationmicroprocessors. To effectively cool these next generationmicroprocessors, it is therefore desirable to provide a cooling systemthat is capable of managing high heat loads.

Pumped liquid cooling systems have been used to provide improved thermalperformance over conventional air cooling systems. Pumped liquid coolingsystems typically include a heat sink attached to the microprocessor, aliquid-to-air heat exchanger, and a pump, all connected by tubing. Athermally conductive liquid coolant is circulated through the system bythe pump. As the liquid passes through channels in the heat sink, heatfrom the hot processor is transferred through the heat sink to thecooler liquid. The heat sink is typically designed to maximize heattransfer by maximizing the surface area of the channels through whichthe liquid passes. For example, micro-channel heat sinks utilize veryfine fin channels through which liquid coolant flows. The hot liquidexiting the heat sink is then circulated through the liquid-to-air heatexchanger before circulating back to the liquid pump for another cycle.Use of closed liquid cooling systems is beginning to migrate from highperformance computers to personal computers. However, even the bestpumped liquid cooling systems are limited in their ability to maintainlow device temperatures without the use of refrigeration and will beunable to satisfy the cooling demands of next-generationmicroprocessors. Without further innovation in the area of coolingsystems, the development of next-generation microprocessors and otherelectronic devices will be hampered.

As noted above, liquid cooling systems commonly rely on flowing liquidwater through channels in finned heat sinks. The heat sinks are oftenindirectly coupled to a heat source via a metal base plate, thermalpaste, such as solder thermal interface material (STIM) or polymerthermal interface material (PTIM), and/or a direct bond adhesive. Whilethis approach can be more effective than air cooling, the interveningmaterials between the water and the heat source (e.g. themicroprocessor) induce significant thermal resistance, which reduces theoverall efficiency of the cooling system. The intervening materials alsoadd cost and time to manufacturing and installation processes,constitute additional points of failure, and create potential disposalissues. Finally, the intervening materials render the system unable toadapt to local hot spots on a heat source. Consequently, the entireliquid cooling system must be designed to accommodate the maximumanticipated heat load of one or more localized hot spots on the surfaceof the heat source (e.g. a surface proximate one hot core of a multicoreprocessor), resulting in additional cost and complexity of the coolingsystem.

Further improvements have been made to liquid cooling systems by usingcoolants other than water. Unlike water, dielectric coolants can beplaced in direct contact with electronic devices and not harm them. Useof such dielectric coolants can eliminate a significant amount ofthermal interface material from the system. However, some dielectriccoolants have a lower heat capacity than water, so more aggressivecooling techniques may be required to achieve a desired performance.

Immersion cooling is an aggressive form of liquid cooling where anentire electronic device is submerged in a vat of dielectric coolant.Unfortunately, immersion cooling requires vats that are large, costly,and heavy, especially when filled with a dielectric coolant. Typically,a room must be specially engineered to accommodate an immersion coolingvat, and containment systems may need to be designed and installed inthe room as a precaution against vat failure. Immersion cooling canrequire large volumes of costly dielectric coolants. Another downside ofimmersion cooling is that certain coolants may act as solvents and, overtime, remove certain identifying information (e.g. printed serialnumbers and model numbers) from electronic components on a motherboard,which can make servicing the computer more difficult.

Another liquid cooling approach involves atomized sprays, in whichatomized liquid coolant is sprayed directly on a surface through air orvapor. As a result, small droplets impinge on the heated surface forminga thin film of liquid directly on the computer chips. Heat is thentransferred from the heated surface to the liquid either by sensibleheating of the bulk liquid or by boiling off of a fraction of the liquid(i.e. latent heating). This method of heat removal is known as spraycooling or spray evaporative cooling and is a very efficient method ofremoving high heat fluxes from small surfaces. Unfortunately, the marginfor error in spray cooling systems is very narrow and the onset of dryout and critical heat flux is a constant concern that can havecatastrophic consequences. Critical heat flux is a condition whereevaporation of coolant from the surface to be cooled prevents atomizedliquid from reaching and cooling the surface, often resulting inrun-away device temperatures and rapid failure.

Spray cooling is limited by several factors. First, spray coolingrequires a significant working volume to enable atomized sprays to form,which results in non-compact cooling components. Second, atomizing theliquid requires a significant amount of pressure upstream of theatomizer to generate an appropriate pressure drop at the atomizer-airinterface to enable atomized sprays to form. Maintaining this amount ofpressure within the system consumes a significant amount of energy.Third, high flow rates of atomized sprays are required to prevent dryout or critical heat flux from occurring. In the end, it has provendifficult to design a practical and compact spray cooling system,despite a large amount of time and effort that has been expended to doso.

Another liquid cooling approach involves direct jet impingement, wherestreams of liquid are projected through a liquid medium and impingedirectly on a surface to be cooled. While impinging jets are known tohave notable heat transfer performance, impinging jet systems haveproblems of scalability. To achieve high heat transfer over a largearea, arrays of jets must be used. The use of arrays in conventionaldirect jet impingement systems, however, is problematic. Opposingsurface flows of fluid from neighboring jet streams emitted from thearray of jets can induce stagnant regions on the surface to be cooled.Stagnation regions prevent cooler fluid from mixing with warmer fluid inthe stagnation regions, leading to bubble growth and dry out at thesurface being cooled as the warmer fluid experiences phase change. Thus,the interaction of jet streams can lead to inefficient cooling caused byliquid build-up on the heated surface, creating regions of poor heattransfer and non-uniform heat transfer across the surface being cooled.In the regions of poor heat transfer, the surface temperatures can risesignificantly above the average surface temperature, causing the surfacetemperature in these regions to run away, leading to catastrophicfailure of the device being cooled.

Conventional jet impingement systems use nozzles that are part of alarge, flat nozzle plate. As fluid from jet streams impinging on thesurface being cooled flow outward from the center of the surface, thefluid can have sufficient momentum to completely deflect the outermostjets, preventing the outermost jests from impinging on the heatedsurface near its edge. As a result of these factors, conventionalimpinging jet systems are limited in size and performance. In addition,existing nozzle plates can be costly and complex to manufacture.

In view of the foregoing discussion, efficient, scalable,high-performing methods and apparatuses are needed for cooling surfacesof devices, such as next-generation microprocessors and electroniccircuitry that produce high heat loads.

SUMMARY

This disclosure presents methods, apparatuses, and assemblies forcooling one or more heat sources, such as one or more heat sourcesassociated with an electrical, mechanical, chemical, orelectromechanical device or process.

In one example, a method of cooling two heat-providing surfaces within aserver using a cooling apparatus having two series-connected heat sinkmodules can include providing a flow of single-phase liquid coolant toan inlet port of a first heat sink module mounted on a firstheat-providing surface within a server. A first amount of heat can betransferred from the first heat-providing surface to the single-phaseliquid coolant resulting in vaporization of a portion of the singlephase liquid coolant thereby changing the flow of single-phase liquidcoolant to two-phase bubbly flow containing liquid coolant with vaporcoolant dispersed as bubbles in the liquid coolant. The two-phase bubblyflow can have a first quality. The method can include transporting thetwo-phase bubbly flow from an outlet port of the first heat sink moduleto an inlet port of a second heat sink module. The second heat sinkmodule can be mounted on a second heat-providing surface within theserver. A second amount of heat can be transferred from the secondheat-providing surface to the two-phase bubbly flow resulting invaporization of a portion of the liquid coolant within the two-phasebubbly flow thereby resulting in a change from the first quality to asecond quality. The second quality can be higher than the first quality.The energy from the first amount of heat and the second amount of heatcan be stored, at least in part, as latent heat in the two-phase bubblyflow and transported out of the server through the cooling apparatus.The amount of heat transferred out of the server can be a function ofthe amount of vapor formed within the two-phase bubbly flow and the heatof vaporization of the coolant.

Providing the flow of single-phase liquid coolant to the inlet port ofthe first heat sink module can include providing a flow rate of about0.1-10, 0.2-5, 0.3-2.5, 0.6-1.2, or 0.8-1.1 liters per minute ofsingle-phase liquid coolant to the first inlet of the first heat sinkmodule. The flow of single-phase liquid coolant can be a dielectriccoolant such as, for example, HFE-7000, R-245fa, HFE-7100 or acombination thereof.

Providing flow of single-phase liquid coolant to the first heat sinkmodule can include providing the single-phase flow of coolant at apredetermined temperature and a predetermined pressure, where thepredetermined temperature is slightly below the saturation temperatureof the single-phase liquid coolant at the predetermined pressure. Thepredetermined temperature can be about 0.5-20, 0.5-15, 0.5-10, 0.5-7,0.5-5, 0.5-3, 0.5-1, 1-20, 1-15, 1-10, 1-7, 1-5, 1-3, 3-20, 3-15, 3-10,3-7, 3-5, 5-20, 5-15, 5-10, 5-7, 7-20, 7-15, 7-10, 10-20, 10-15, or15-20 degrees C. below the saturation temperature of the single-phaseliquid coolant at the predetermined pressure.

A pressure differential of about 0.5-5.0, 0.5-3, or 1-3 psi can bemaintained between the inlet port of the first heat sink module and theoutlet port of the first heat sink module. The pressure differential canbe suitable to promote the coolant to advance from the inlet port of thefirst heat sink module to the outlet port of the first heat sink module.

A saturation temperature and pressure of the two-phase flow having asecond quality can be less than a saturation temperature and pressure ofthe two-phase flow having a first quality, thereby allowing the secondheat-providing surface to be maintained at a lower temperature than thefirst heat-providing surface when a first heat flux from the firstheat-providing surface is approximately equal to a second heat flux fromthe second heat-providing surface.

The first quality can be about 0-0.1, 0.05-0.15, 0.1-0.2, 0.15-0.25,0.2-0.3, 0.25-0.35, 0.3-0.4, 0.35-0.45, 0.4-0.5, 0.45-0.55, and thesecond quality can be greater than the first quality, such as, forexample, 0-0.1, 0.05-0.15, 0.1-0.2, 0.15-0.25, 0.2-0.3, 0.25-0.35,0.3-0.4, or 0.4-0.45 greater than the first quality.

The liquid portion of the two-phase bubbly flow that is transportedbetween the first heat sink module and the second heat sink module canhave a temperature slightly below its saturation temperature. Thepressure of the two-phase bubbly flow can be about 0.5-5.0, 0.5-3, or1-3 psi less than the predetermined pressure of flow of single-phaseliquid coolant provided to the inlet port of the first heat sink module.

The first heat-providing surface can be a surface of a microprocessorwithin the server. The first heat-providing surface can be a surface ofa thermally conductive base member in thermal communication with amicroprocessor within the server. The thermally conductive base membercan be a metallic base plate mounted on the microprocessor using athermal interface material.

In another example, a method of cooling two or more heat-providingsurfaces using a cooling apparatus comprising two or more fluidlyconnected heat sink modules arranged in a series configuration caninclude providing a flow of single-phase liquid coolant to a first inletport of a first heat sink module mounted on a first surface to becooled. The flow of single-phase liquid coolant can have a predeterminedpressure and a predetermined temperature at the first inlet port of thefirst heat sink module. The predetermined temperature can be slightlybelow a saturation temperature of the coolant at the predeterminedpressure. The method can include projecting the flow of single-phaseliquid coolant against the first heat-providing surface within the firstheat sink module, where a first amount of heat is transferred from thefirst heat-providing surface to the flow of single-phase liquid coolantthereby inducing phase change in a portion of the flow of single-phaseliquid coolant and thereby changing the flow of single-phase liquidcoolant to two-phase bubbly flow containing a liquid coolant and aplurality of vapor bubbles dispersed within the liquid coolant. Theplurality of vapor bubbles can have a first number density.

The method can include providing a second heat sink module mounted on asecond heat-providing surface. The second heat sink module can include asecond inlet port and a second outlet port. The method can includeproviding a first section of tubing having a first end connected to thefirst outlet port of the first heat sink module and a second endconnected to the second inlet port of the second heat sink module. Thefirst section of tubing can transport the two-phase bubbly flow havingthe first number density from the first outlet port of the first heatsink module to the second inlet port of the second heat sink module. Themethod can include projecting the two-phase bubbly flow having the firstnumber density against the second heat-providing surface within thesecond heat sink module, where a second amount of heat is transferredfrom the second heat-providing surface to the two-phase bubbly flowhaving a first number density and thereby changing two-phase bubbly flowhaving a first number density to a two-phase bubbly flow having a secondnumber density greater than the first number density.

A saturation temperature and pressure of the two-phase flow having asecond number density can be less than a saturation temperature andpressure of the two-phase flow having a first number density, therebyallowing the second heat-providing surface to be maintained at a lowertemperature than the first heat-providing surface when a first heat fluxfrom the first heat-providing surface is approximately equal to a secondheat flux from the second heat-providing surface.

The predetermined temperature of the flow of single-phase liquid coolantat the first inlet port of the first heat sink module can be about0.5-20, 0.5-15, 0.5-10, 0.5-7, 0.5-5, 0.5-3, 0.5-1, 1-20, 1-15, 1-10,1-7, 1-5, 1-3, 3-20, 3-15, 3-10, 3-7, 3-5, 5-20, 5-15, 5-10, 5-7, 7-20,7-15, 7-10, 10-20, 10-15, or 15-20 degrees C. below the saturationtemperature of the flow of single-phase liquid coolant at thepredetermined pressure of the flow of single-phase liquid coolant at thefirst inlet of the first heat sink module.

Providing the flow of single-phase liquid coolant to the inlet port ofthe first heat sink module can include providing a flow rate of about0.1-10, 0.2-5, 0.3-2.5, 0.6-1.2, or 0.8-1.1 liters per minute ofsingle-phase liquid coolant to the first inlet port of the first heatsink module.

The liquid in the two-phase bubbly flow being transported between thefirst heat sink module and the second heat sink module can have atemperature at or slightly below its saturation temperature, wherein apressure of the two-phase bubbly flow having a first number density isabout 0.5-5.0, 0.5-3, or 1-3 psi less than the predetermined pressure ofthe flow of single-phase liquid coolant provided to the first heat sinkmodule.

The first heat sink module can include an inlet chamber formed withinthe first heat sink module and an outlet chamber formed within the firstheat sink module. The outlet chamber can have an open portion enclosedby the first surface to be cooled when the first heat sink module ismounted on the surface to be cooled. The first heat sink module caninclude a plurality of orifices extending from the inlet chamber to theoutlet chamber. Projecting the flow of single-phase liquid coolantagainst the first heat-providing surface can include projecting aplurality of jet streams of single-phase coolant through the pluralityof orifices into the outlet chamber and against the first surface to becooled when the flow of single-phase liquid coolant is provided to theinlet chamber from the first inlet port of the first heat sink module.The first plurality of orifices can have an average diameter of about0.001-0.020, 0.001-0.2, 0.001-0.150, 0.001-0.120, 0.001-0.005, or0.030-0.050 inches. Outlets of the plurality of orifices can be arrangedat a jet height from the first surface to be cooled. The jet height canbe about 0.01-0.75, 0.05-0.5, 0.05-0.25, 0.020-0.25, 0.03-0.125, or0.04-0.08 inches. At least one orifice can have a central axis arrangedat an angle of about 30-60, 40-50, or 45 degrees with respect to thefirst surface to be cooled.

In another example, a method of cooling two microprocessors on amotherboard using a two-phase cooling apparatus comprising twoseries-connected heat sink modules can include providing a flow ofsingle-phase liquid coolant to an inlet port of a first heat sink modulemounted on a first thermally conductive base member. The first thermallyconductive base member can be mounted on a first microprocessor on amotherboard, where heat is transferred from the first microprocessorthrough the first thermally conductive base member and to the flow ofsingle-phase liquid coolant resulting in boiling of a first portion ofthe coolant, thereby changing the flow of single-phase liquid coolant totwo-phase bubbly flow having a first quality. The method can includetransporting the two-phase bubbly flow from an outlet port of the firstheat sink module to an inlet port of a second heat sink module throughflexible tubing. The second heat sink module can be mounted on a secondthermally conductive base member that is mounted on a secondmicroprocessor on the motherboard. Heat can be transferred from thesecond microprocessor through the second thermally conductive basemember and to the two-phase bubbly flow resulting in vaporization of asecond portion of the coolant within the two-phase bubbly flow therebyresulting in a change from the first quality to a second quality, thesecond quality being higher than the first quality.

Additional objects and features of the invention are introduced below inthe Detailed Description and shown in the drawings. While multipleembodiments are disclosed, still other embodiments will become apparentto those skilled in the art from the following Detailed Description,which shows and describes illustrative embodiments. As will be realized,the disclosed embodiments are susceptible to modifications in variousaspects, all without departing from the scope of the present disclosure.Accordingly, the drawings and detailed description are to be regarded asillustrative in nature and not restrictive.

This Summary is provided to introduce a selection of concepts in asimplified form that are further described in the Detailed Descriptionbelow. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intendedthat this Summary be used to limit the scope of the claimed subjectmatter. Furthermore, the claimed subject matter is not limited toimplementations that solve any or all disadvantages noted in any part ofthis disclosure.

BRIEF DESCRIPTIONS OF DRAWINGS

FIG. 1 shows a front perspective view of a cooling apparatus installedon a row of server racks in a data center.

FIG. 2A shows a rear view of the cooling apparatus of FIG. 1.

FIG. 2B shows a detailed view of a portion of the cooling apparatus ofFIG. 2A, where the pump, reservoir, heat exchanger, inlet manifold ofthe primary cooling loop, and sections of flexible tubing are visible.

FIG. 3 shows a left side view of the cooling apparatus of FIG. 1, wherethe pump, reservoir, heat exchanger, pressure regulator, first bypass,and a portion of the primary cooling loop are visible.

FIG. 4 shows an inlet manifold and an outlet manifold of the coolingapparatus and sections of flexible tubing with quick-connect fittingsconnecting parallel cooling lines to the inlet and outlet manifolds.

FIG. 5 shows a top perspective view of a server with its lid removed anda portion of a cooling apparatus installed within the server, thecooling apparatus having a two heat sink modules mounted onvertically-arranged heat-generating components within the server, theheat sink modules arranged in a series configuration and fluidlyconnected with sections of flexible tubing to transport coolant from anoutlet port of a first heat sink module to an inlet port of a secondheat sink module.

FIG. 6 shows a top view of a server with its lid removed and a portionof a cooling apparatus installed within the server, the coolingapparatus including two heat sink modules mounted onhorizontally-oriented microprocessors within the server, the heat sinkmodules arranged in a series configuration and fluidly connected with asection of flexible tubing to transport coolant from an outlet port of afirst heat sink module to an inlet port of a second heat sink module.

FIG. 7 shows a cooling assembly including a heat sink module, a firstsection of flexible tubing fluidly connected to an inlet port of theheat sink module, and a second section of flexible tubing fluidlyconnected to an outlet port of the heat sink module.

FIG. 8 shows a plot of power consumption versus time for a computer roomwith forty active dual-processor servers initially cooled by a CRAC andthen cooled by the CRAC and the cooling apparatus described herein,where the cooling apparatus described herein provides substantialreductions in power consumption despite being installed on just ten ofthe forty servers in the computer room.

FIG. 9 shows a front perspective view of a redundant cooling apparatusinstalled on eight racks of servers in a data center where the redundantcooling apparatus includes two fully independent primary cooling loops.

FIG. 10 shows a rear view of the redundant cooling apparatus of FIG. 9.

FIG. 11A shows a schematic of a cooling apparatus having one heat sinkmodule mounted on a heat-generating surface and fluidly connected to aprimary cooling loop.

FIG. 11B shows the schematic of FIG. 11A with a primary cooling loopidentified by dashed lines.

FIG. 11C shows the schematic of FIG. 11A with a first bypass identifiedby dashed lines.

FIG. 11D shows the schematic of FIG. 11A with a second bypass identifiedby dashed lines.

FIG. 12A shows a schematic of a cooling apparatus having one heat sinkmodule mounted on a heat source and a pressure regulator locateddownstream of the heat exchanger in the first bypass.

FIG. 12B shows a schematic of a cooling apparatus having two pumpsarranged in parallel for redundancy in case one pump fails.

FIG. 12C shows a schematic of a cooling apparatus having a three-wayvalve at a junction between the primary cooling loop and the bypass.

FIG. 12D shows a schematic of a cooling apparatus having a three-wayvalve at the junction between the primary cooling loop and the bypass,where the bypass contains a heat exchanger.

FIG. 12E shows a schematic of a cooling apparatus including a firstbypass and a primary cooling loop where the primary cooling loopincludes a heat sink module with an internal bypass having a pressureregulator.

FIG. 12F shows a schematic of a cooling apparatus having a primarycooling loop and one bypass.

FIG. 12G shows a schematic of a cooling apparatus where the primarycooling loop includes a heat sink module with an internal bypass havinga pressure regulator.

FIG. 12H shows a schematic of a cooling apparatus including a pump,reservoir, and a heat sink module that is configured to mount on a heatsource or be mounted in thermal communication with a heat source.

FIG. 12I shows a schematic of a cooling apparatus including a pump and aheat sink module that is configured to mount on a heat source or bemounted in thermal communication with a heat source.

FIG. 12J shows a schematic of a cooling apparatus with a primary coolingloop, a first bypass, and a second bypass, where the primary coolingloop includes a first pump, and the first bypass includes a second pump.

FIG. 12K shows a schematic of a cooling apparatus with a primary coolingloop, a first bypass, and a second bypass, where the primary coolingloop includes a first pump, and the second bypass includes a secondpump.

FIG. 12L shows a schematic of a cooling apparatus with a primary coolingloop, a first bypass, and a second bypass, where the primary coolingloop includes a first pump, the first bypass includes a second pump, andthe second bypass includes a third pump.

FIG. 12M shows a schematic of a cooling apparatus with a primary coolingloop, a first bypass, and a second bypass, where the first bypassincludes a first heat exchanger, and the second bypass includes a secondheat exchanger.

FIG. 12N shows a schematic of a cooling apparatus having a primarycooling loop, a first bypass, and a second bypass, where the firstbypass and second bypass merge upstream of a reservoir.

FIG. 12O shows a schematic of a cooling apparatus having a primarycooling loop, a first bypass, and a second bypass, where the firstbypass and second bypass merge upstream of a reservoir and upstream of aheat exchanger.

FIG. 12P shows a schematic of a cooling apparatus having a primarycooling loop with redundant pumps, a first bypass, and a second bypass,where the second bypass is connected to a heat exchanger that can be arooftop dry cooler.

FIG. 12Q shows a schematic of a cooling apparatus having a primarycooling loop and a bypass, where the bypass is connected to a heatexchanger that can be a rooftop dry cooler.

FIG. 12R shows a schematic of a cooling apparatus having a primarycooling loop having a pump, a reservoir, and a heat sink module mountedon a surface to be cooled.

FIG. 12S shows a schematic of a cooling apparatus having a primarycooling loop, a first bypass, and a second bypass, where the firstbypass includes a first heat exchanger, and where the primary coolingloop includes two series-connected heat sink modules with a second heatexchanger fluidly connected between the heat sink modules to, forexample, avoid formation of slug flow in the primary cooling loopbetween the heat sink modules.

FIG. 12T shows a schematic of a cooling apparatus configured to cool tworacks of servers, the cooling apparatus including an inlet manifold andan outlet manifold for each rack of servers, where a plurality of heatsink modules are fluidly connected in series and parallel arrangementsbetween each inlet and outlet manifold to cool hot spots within theservers.

FIG. 13 shows a schematic of a cooling apparatus including a filterlocated between the reservoir and a pump inlet in the primary coolingloop.

FIG. 14A shows a schematic of a cooling apparatus having three heat sinkmodules arranged in a series configuration on three surfaces to becooled.

FIG. 14B shows a representation of coolant flowing through three heatsink modules connected in series by lengths of tubing, similar to theconfigurations shown in FIGS. 14A and 15, and also shows correspondingplots of saturation temperature, liquid coolant temperature, pressure,and quality (x) versus distance, where quality increases, pressuredecreases, liquid coolant temperature decreases, and T_(sat) decreasesthrough successive series-connected heat sink modules.

FIG. 14C shows a representation of coolant flowing through three heatsink modules connected in series by lengths of tubing, similar to FIG.14B, except that the coolant does not reach its saturation temperatureuntil the second heat sink module.

FIG. 15 shows a portion of a primary cooling loop of a coolingapparatus, where the cooling loop includes three series-connected heatsink modules mounted on three surfaces to be cooled and connected bysections of flexible tubing where a single-phase liquid coolant isprovided to a first heat sink module, and due to heat transfer occurringwithin the first module, two-phase bubbly flow is transported from thefirst module to the second module, and due to heat transfer occurringwithin the second module, higher quality two-phase bubbly flow istransported from the second module to the third module, and due to heattransfer occurring within the third module, even higher qualitytwo-phase bubbly flow is transported out of the third module.

FIG. 16 shows a schematic of a cooling apparatus with a primary coolingloop that includes three parallel cooling lines where each parallelcooling line includes three heat sink modules fluidly connected inseries.

FIG. 17 shows a schematic of a redundant cooling apparatus having aredundant heat sink module mounted on a surface to be cooled.

FIG. 18 shows a schematic of a redundant cooling apparatus with a firstprimary cooling loop that includes two parallel cooling lines where eachparallel cooling line is fluidly connected to three redundant heat sinkmodules arranged in series, and a second primary cooling loop thatincludes two parallel cooling lines where each parallel cooling line isfluidly connected to three redundant heat sink modules arranged inseries.

FIG. 19 shows a top view of a redundant cooling apparatus installed in adata center having twenty racks of servers, the redundant cooling systembeing connected to heat exchangers located inside of the room where thedata center is located.

FIG. 20 shows a top view of a redundant cooling apparatus installed in adata center having twenty racks of servers, the redundant cooling systembeing connected to heat exchangers located outside of the room where thedata center is located.

FIG. 21 shows a top perspective view of a compact heat sink module forcooling a heat source.

FIG. 22 shows a top view of heat sink module of FIG. 21, the heat sinkmodule including a first compression fitting installed on an inlet portof the heat sink module, a second compression fitting installed on anoutlet port of the heat sink module, and a plurality of fastenersarranged near a perimeter of the heat sink module and according to amounting pattern for mounting the heat sink module to a heat-providingsurface.

FIG. 23 shows a bottom perspective view of the heat sink module of FIG.21 showing an inlet port, outlet port, outlet chamber, mounting holes,dividing member, and a plurality of orifices in the dividing member, aswell as a sealing member installed within a continuous channelcircumscribing the outlet chamber of the heat sink module.

FIG. 24 shows a bottom view of the heat sink module of FIG. 21.

FIG. 25 shows a side cross-sectional view of the heat sink module ofFIG. 24 taken along section B-B and showing an inlet port, inletpassage, inlet chamber, a plurality of orifices, and outlet chamberwithin the heat sink module.

FIG. 26 shows a side cross-sectional view of the heat sink module ofFIG. 24 taken along section B-B with the heat sink module being mountedon a thermally conductive base member and showing central axes of theplurality of orifices and bubble formation within the outlet chamberproximate the surface of the thermally conductive base member.

FIG. 27 shows a side cross-sectional view of the heat sink module ofFIG. 24 taken along section B-B with the heat sink module mounted on acomputer processor located on a motherboard and showing central axes ofthe plurality of orifices.

FIG. 28 shows a side cross-sectional view of the heat sink module ofFIG. 24 taken along section B-B with the heat sink module mounted on athermally conductive base member that is attached to a microprocessor bya layer of thermal interface material, the microprocessor beingelectrically connected to a motherboard.

FIG. 29 shows a side cross-sectional view of the heat sink module ofFIG. 24 taken along section A-A and showing an inlet port, outlet port,outlet passage, outlet chamber, and a plurality of orifices within theheat sink module.

FIG. 30 shows a side cross-sectional view of the heat sink module ofFIG. 24 taken along section A-A, with the heat sink module mounted on athermally conductive base member and showing central axes of theplurality of orifices and bubbles forming within the outlet chamberproximate the surface of the conductive base member and exiting themodule through the outlet port as part of a two-phase bubbly flow.

FIG. 31 shows a top cross-sectional view of the heat sink module of FIG.21 taken along section C-C shown in FIG. 25, the cross-section passinghorizontally through a dividing member of the heat sink module to exposean array of orifices within the heat sink module, the orifices arrangedaccording to staggered columns and staggered TOWS.

FIG. 32 shows a top view of a surface to be cooled within an outletchamber of a heat sink module of FIG. 21 taken along section D-D shownin FIG. 30, where an array of jet streams originating from the pluralityof orifices of the heat sink module are impinging non-perpendicularly onthe surface to be cooled, thereby creating a directional flow of coolantfrom left to right across the surface to be cooled, the directional flowtraveling toward an outlet port of the heat sink module.

FIG. 33 shows a bottom view of a heat sink module having a firstplurality of orifices and a second plurality of orifices, the secondplurality of orifices being configured to deliver a plurality ofanti-pooling jet streams into the outlet chamber.

FIG. 34 shows a side cross-sectional view of the heat sink module ofFIG. 33 taken along section B-B, the side view showing an inlet port,inlet passage, inlet chamber, plurality of orifices, outlet chamber, andanti-pooling orifice within the heat sink module.

FIG. 35 shows a detailed view of a portion of the heat sink module ofFIG. 34 highlighting the anti-pooling orifice that extends from theinlet chamber to a rear wall of the outlet chamber.

FIG. 36 shows a side cross-sectional view of the heat sink module ofFIG. 33 taken along section B-B, with the heat sink module mounted on athermally conductive base member and showing central axes of theplurality of orifices and the anti-pooling orifice.

FIG. 37 shows a side cross-sectional view of the heat sink module ofFIG. 33 taken along section A-A and showing an outlet port, outletpassage, inlet chamber, outlet chamber, plurality of orifices, andanti-pooling orifice.

FIG. 38 shows a side cross-sectional view of the heat sink module ofFIG. 33 taken along section A-A, with the heat sink module mounted on athermally conductive base member and showing central axes of theplurality of orifices and the anti-pooling orifice.

FIG. 39 shows a top view of a heat sink module having a plurality ofanti-pooling orifices.

FIG. 40 shows a side cross-sectional view of the heat sink module ofFIG. 39 taken along section B-B and showing the location of section C-Cpassing through the inlet chamber and the location of section D-Dpassing through the outlet chamber.

FIG. 41 shows a front view of the heat sink module of FIG. 39.

FIG. 42 shows a left side view of the heat sink module of FIG. 39showing the outlet and inlet ports having an angle of a with respect toa mounting surface of the heat sink module.

FIG. 43 shows a top view of the heat sink module of FIG. 39 taken alongsection C-C shown in FIG. 42, the top view showing the inlet port, inletpassage, inlet chamber, top surface of the dividing member, plurality oforifices, and plurality of anti-pooling orifices.

FIG. 44 shows a bottom view of the heat sink module of FIG. 39 takenalong section D-D shown in FIG. 42, the bottom view showing the outletport, outlet passage, outlet chamber, bottom surface of the dividingmember, plurality of orifices, and plurality of anti-pooling orifices.

FIG. 45 shows a bottom view of a heat sink module having a plurality ofboiling-inducing members within an outlet chamber.

FIG. 46 shows a side cross-sectional view of the heat sink module ofFIG. 45 taken along section B-B, the side view showing an inlet port,inlet passage, inlet chamber, plurality of orifices, dividing member,and plurality of boiling-inducing members.

FIG. 47 shows a side cross-sectional view of the heat sink module ofFIG. 45 taken along section B-B with the heat sink module mounted on athermally conductive base member and showing central axes of theplurality of orifices.

FIG. 48 shows a detailed view of a portion of the heat sink module shownin FIG. 46, the detailed view showing three boiling inducing membersextending from a bottom surface of the dividing member into the outletchamber and an orifice extending from the inlet chamber to the outletchamber.

FIG. 49 shows a side cross-sectional view of the heat sink module ofFIG. 45 taken along section A-A, the side view showing an outlet port,outlet passage, outlet chamber, inlet chamber, plurality of orifices,plurality of boiling-inducing member, and dividing member.

FIG. 50 shows a side cross-sectional view of the heat sink module ofFIG. 45 taken along section A-A, the heat sink module being mounted on athermally conductive base member and showing central axes of theplurality of orifices.

FIG. 51A shows a top perspective view of a redundant heat sink modulehaving a first independent flow path and a second independent flow path.

FIG. 51B shows a top view of the redundant heat sink module of FIG. 51A,where the first independent flow path and the second independent flowpath are represented by dashed lines, where the first independent flowpath passes through a first region near a middle of the module, andwhere the second independent flow path passes through a second regionbeyond the perimeter of the first region.

FIG. 51C shows a top view of the redundant heat sink module of FIG. 51Awith connectors installed on the inlet and outlet ports.

FIG. 51D shows a bottom view of the redundant heat sink module of FIG.51A, where the first independent flow path includes an array of orificesarranged in a first region located near a middle of the module, andwhere the second independent flow path includes an array of orificesarranged in a second region beyond the perimeter of the first region.

FIG. 51E shows a top view of the heat sink module of FIG. 51A.

FIG. 51F shows a side cross-sectional view of the redundant heat sinkmodule of FIG. 51A taken along section A-A shown in FIG. 51E.

FIG. 51G shows a side cross-section view of the redundant heat sinkmodule of FIG. 51A taken along section B-B shown in FIG. 51E.

FIG. 51H shows a side view of the redundant heat sink module of FIG.51A.

FIG. 51I shows a cross-sectional view of the redundant heat sink moduleof FIG. 51A taken along section C-C shown in FIG. 51H.

FIG. 51J shows a top view of the redundant heat sink module of FIG. 51A.

FIG. 51K shows a side cross-sectional view of the redundant heat sinkmodule of FIG. 51A taken along section D-D shown in FIG. 51J.

FIG. 51L shows a top view of the redundant heat sink module of FIG. 51A.

FIG. 51M shows a side cross-section view of the redundant heat sinkmodule of FIG. 51A taken along section E-E of FIG. 51L.

FIG. 52A shows two redundant heat sink modules mounted on a thermallyconductive base member, where two sink modules are provided forredundancy and/or increased heat transfer capability.

FIG. 52B shows two heat sink modules mounted on a thermally conductivebase member, where two sink modules are provided for redundancy and/orincreased heat transfer capability.

FIG. 53 shows a top perspective view of a redundant heat sink modulehaving side-by-side independent flow paths, a first independent flowpath having an inlet port and an outlet port, and a second independentflow path having an inlet port and an outlet port.

FIG. 54 shows a bottom perspective view of a redundant heat sink mountedto a planar, thermally conductive base member with a plurality offasteners.

FIG. 55 shows a top perspective view of a thermally conductive basemember having a top surface and an array of boiling-inducing membersextending from the top surface.

FIG. 56 shows a top perspective view of a motherboard for a serverincluding microprocessors and a plurality of vertically arranged memorymodules that are parallel and offset, where a heat sink module can bemounted on top of each microprocessor.

FIG. 57 shows a top perspective view of a server including a pluralityof vertically arranged memory modules that are parallel and offset.

FIG. 58 shows two-phase flow regimes, including (a) bubbly flow with afirst number density of bubbles, (b) bubbly flow with a second numberdensity of bubbles that is greater than the first number density, (c)slug flow, (d) churn flow, and (e) annular flow.

FIG. 59A shows a flow regime map for a steam-water system and showsρ_(liquid)*j_(liquid) ² on the x-axis and ρ_(vapor)*j_(vapor) ² on they-axis.

FIG. 59B shows two-phase flow regimes, including bubbly flow, plotted onvoid fraction versus mass flux axes.

FIG. 60 shows a flow boiling curve where heat transfer rate is plottedas a function of excess temperature.

FIG. 61 shows a boiling curve for water at 1 atm showing an onset ofnucleate boiling, an inflection point, the point of critical heat flux,and the Leidenfrost point.

FIG. 62 shows possible orifice configurations for a heat sink module,including (a) a regular rectangular jet array, (b) a regular hexagonaljet array, and (c) a circular jet array.

FIG. 63 shows a top view of a heated surface covered by coolant, thecoolant having regions of vapor coolant and wetted regions of liquidcoolant in contact with the heated surface, where a contact line lengthis measured as a sum of all curves where liquid coolant, vapor coolant,and the heated surface are in mutual contact on the heated surface.

FIG. 64 shows a plot of CPU power consumption versus junctiontemperature for processor switching speeds of 1.6 GHz and 2.4 GHz.

FIG. 65 shows a heat sink module with an insertable orifice plateinstalled within a module body.

FIG. 66 shows a side cross-sectional view of a server having a firstmicroprocessor, a second microprocessor, a first finned heat sinkarranged on top of the first microprocessor, a second finned heat sinkarranged on top of the second microprocessor, and a cooling system,where the cooling system includes a heat sink module attached to athermally conductive member that extends from the first finned heat sinkto the second heat sink module.

FIG. 67 shows a side cross-sectional view of a server having a firstmicroprocessor, a second microprocessor, and a cooling system, where thecooling system includes a heat sink module attached to a thermallyconductive member that extends from the first microprocessor to thesecond microprocessor.

FIG. 68 shows a schematic of a cooling apparatus having a primarycooling loop, a bypass, and an independent heat rejection loop.

FIG. 69 shows a schematic of a cooling apparatus having a first coolingloop, a second cooling loop, and an independent heat rejection loop.

FIG. 70 shows a schematic of a cooling apparatus having a redundant heatsink module mounted on a heat source, the cooling apparatus having afirst cooling loop and a second cooling loop, both fluidly connected toa common reservoir.

FIG. 71 shows a schematic of a cooling apparatus having a primarycooling loop with a pump, heat exchanger, heat sink module, reservoir,and bypass, the bypass having a pressure regulator.

FIG. 72 shows a schematic of a cooling apparatus having a primarycooling loop with redundant pumps and check valves, reservoir, heatexchanger, heat sink module, and bypass, the bypass having a pressureregulator used to control the pressure differential between the inletand outlet ports of the heat sink module.

FIG. 73 shows a cross-sectional view of a first heat sink module fluidlyconnected to a second heat sink module by a section of flexible tubing,where single-phase flow becomes two-phase bubbly flow within an outletchamber of the first heat sink module due to heat transferred from afirst surface to be cooled to the flow, where flexible tubing transportsthe two-phase bubbly flow from an outlet port of the first heat sinkmodule to an inlet port of a second heat sink module, where thetwo-phase bubbly flow is delivered to an inlet chamber of the secondheat sink module and passes as a plurality of jet streams through aplurality of orifices within the second heat sink module and impingeagainst a second surface to be cooled.

FIG. 74 shows a portable cooling device that includes a plurality ofheat sink modules mounted on a portable layer, the portable layer beingrigid or conformable to a contoured heated surface and including one ormore inlet connections and one or more outlet connections that can beconnected to a cooling apparatus that delivers a flow of pressurizedcoolant to the portable cooling device to permit cooling of the heatedsurface through latent heating of the coolant within the plurality ofheat sink modules.

DETAILED DESCRIPTION

The cooling apparatuses 1 and methods described herein are suitable fora wide variety of applications, ranging from cooling electrical devicesto cooling mechanical devices to cooling chemical reactions and/orprocesses. Examples of electrical devices that can be effectively cooledwith the cooling apparatuses 1 and methods include densely packedservers in data centers, medical imaging devices, solar panels,high-power diode laser arrays, and electric vehicle components (e.g.battery packs, electric motors, and power electronics). Examples ofmechanical devices that can be effectively cooled with the coolingapparatuses 1 and methods include turbines, internal combustion engines,turbochargers, after-treatment components, and braking systems. Examplesof chemical processes that can be effectively cooled with the coolingapparatuses 1 include condensation processes involving rotaryevaporators or reflux distillation condensers.

Compared to competing air or liquid cooling systems, the coolingapparatuses 1 and methods described herein consume less energy, havehigher reliability, operate more safely, are less expensive, and havelower operating noise. The cooling apparatuses 1 described herein aresuitable for retrofit on existing systems or can be incorporated intonew systems. Due to its high efficiency, modularity, flexibleconnections, small size, and hot-swappability, the cooling apparatus 1described herein redefines design constraints that have until nowhampered the progress of new servers and other electronic devices. Thecooling apparatus 1 described herein will allow the size of electronicdevice housings to be significantly reduced while simultaneouslyreducing the risk of overheating of critical components and maintainingor even improving device performance. Using the methods and componentsdescribed herein, a high-efficiency cooling apparatus 1 for a widevariety of applications can be rapidly optimized, manufactured, andinstalled. In some examples, additive-manufacturing processes can beused to rapidly manufacture heat sink modules 100 that permit consistentcooling of multiple device surfaces 12, even where heat distributions onthose surfaces are non-uniform, such as on multi-core microprocessors.

Due to their small size and flexible connections, the componentsdescribed herein can be discretely packaged in many existing machinesand devices that require efficient and reliable cooling of surfaces thatproduce high heat fluxes. For example, the cooling apparatuses 1described herein can be discretely packaged in personal computers orservers to cool microprocessors and memory modules, in vehicles to coolbattery packs, electric motors, and power electronics, and in medicalimaging devices to cool power supplies and other electronic components.

In data center applications, the cooling apparatuses 1 and methodsdescribed herein can provide local, efficient cooling of critical systemcomponents and, where the data center 425 is located in an officebuilding, can allow the ambient temperature of the office building toremain at a temperature that is comfortable for human occupants, whilestill permitting effective cooling of critical system components.Presently, competing air cooling systems use room air within the officebuilding to cool critical system components by employing small fans toblow the air across finned surfaces of the system components. As thesystem components (e.g. microprocessors) are more highly utilized, theybegin to generate more heat. To provide additional cooling, there aretwo options in competing air cooling systems. First, the mass flow rateof room air across the components can be increased to increase the heattransfer rate, or second, the temperature of the room air can be reducedto provide a larger temperature differential between the room air andthe component temperature, thereby increasing the heat transfer rate.Initially, fans speeds can be increased to provide higher flow rates ofroom air, which in turn provides higher heat transfer rates. However, atsome point, maximum fan speeds will be attained, at which point the flowrate of room air can no longer be increased. At this point, if criticalsystem components demand additional cooling (e.g. to prevent overheatingor failure), the only option in competing air cooling systems is todecrease the temperature of the room air by delivering larger volumetricflow rates of cool air from an air conditioning unit to the room toreduce the room temperature. This approach is highly inefficient andultimately results in discomfort for human occupants of the officebuilding, since larger volumetric flow rates of cool air eventuallycause the air temperature within the building to reach an uncomfortablycool temperature, which can diminish worker productivity.

Two-Phase Flow Capability

In some aspects, the cooling apparatuses 1 described herein can beconfigured to cool a heat-generating surface 12 by flowing coolant 50over the surface 12, directing jet streams 16 of coolant against thesurface 12, or a combination thereof (as shown in FIGS. 26 and 30). Theterms “heat-generating surface,” “surface to be cooled,” “surface of thedevice,” “heat source,” “heated surface,” “heat providing surface,”“device surface,” “component surface,” and “heat-producing surface” areused herein to describe any surface 12 of a component or device that isat a temperature above ambient temperature, whether due to heat producedby or within the component or device or due to heat transferred to thecomponent or device from some other component or device that is inthermal communication with the surface 12. Within some components of thecooling apparatus 1, at least a portion of the coolant 50 can undergo aphase change from a liquid to a vapor in response to absorbing heat fromthe surface 12 of the device. The phase change can result in the coolant50 transitioning from a single-phase liquid flow to two-phase bubblyflow or from a two-phase bubbly flow having a first number density ofvapor bubbles to two-phase bubbly flow having a second number density ofvapor bubbles, where the second number density is higher than the firstnumber density. By initiating boiling proximate the surface 12 beingcooled, and taking advantage of the highly-effective heat transfermechanisms associated therewith, the cooling apparatuses 1 and methodsdescribed herein can deliver heat transfer rates that far exceed heattransfer rates attainable with traditional liquid cooling or air coolingsystems. By providing dramatically increased heat transfer rates, thecooling apparatus 1 described herein is able to cool devices far moreefficiently than any other existing cooling apparatus, which translatesto significantly lower power consumption by the cooling apparatus 1described herein. Where the cooling apparatus 1 is used in a large scalecooling application, such as a data center, and replaces a conventionalair conditioning system, the cooling apparatus can result in significantsavings on utility bills for a data center operator.

When a heat-generating surface 12 exceeds the saturation temperature ofthe coolant 50, boiling of the coolant proximate (i.e. at or near) theheat-generating surface occurs. This can occur whether the bulk fluidtemperature of the coolant 50 is at or below its saturation temperature.If the bulk fluid temperature is below the saturation temperature of thecoolant 50, boiling is referred to as “local boiling” or “subcooledboiling.” If the bulk fluid temperature of the coolant is equal to thesaturation temperature, then “bulk boiling” is said to occur. Bubblesformed proximate the heat-generating surface 12 depart the surface 12and are transported by the bulk fluid, creating a flow of liquid fluidwith bubbles distributed therein, known as two-phase bubbly flow.Depending on the degree of subcooling, as the bubbly flow passes throughtubing, some or all of the bubbles in the bubbly flow may condense andcollapse as mixing of the fluid and bubbles occurs. As bubbles collapseback to liquid, the bulk fluid temperature rises. In saturated or bulkboiling, where the bulk fluid temperature is near the saturationtemperature, the bubbles 275 distributed in the fluid may not collapseas the bubbly flow passes through tubing and as mixing of the fluid andbubbles occurs.

Two-phase flow can be described based on a volume fraction of vaporpresent in the flow, where the volume fraction of vapor in the flow(α_(vapor)) plus the volume fraction of liquid (α_(liquid)) in the flowis equal to one (α_(vapor)+α_(liquid)=1). The volume fraction of vapor(α_(vapor)) is commonly referred to as “void fraction” even though thevapor volume is filled with low density gas and no true voids exist inthe flow. The volume fraction within a tube, such as a section offlexible tubing 225 between two series-connected heat sink modules 100,can be calculated using the following equation:

α_(vapor) =A _(vapor) /A _(x)

where A_(x) is the total cross-sectional flow area at point x in thetube, and A_(vapor) is the cross-sectional area occupied by vapor atpoint x in the tube. The volumetric flux of vapor (j_(vapor)) in a flow51, also known as the “superficial velocity” of the vapor, can becalculated using the following equation:

j _(vapor)=(ν_(vapor) *A _(vapor))/A _(x)=α_(vapor)*ν_(vapor)

where ν_(vapor) is the velocity of vapor in the tube. In some instances,the velocity of vapor (ν_(vapor)) and the velocity of the liquid(ν_(liquid)) in the flow may not be equal. This inequality in velocitiescan be described as a slip ratio and calculated using the followingequation:

S=ν _(vapor)/ν_(liquid)

Where the vapor velocity (ν_(vapor)) and the liquid velocity(ν_(liquid)) in the flow are equal, the slip ratio (S) is one. The flowquality is the flow fraction of vapor and is always between zero andone. Flow quality (x) is defined as:

x=m _(vapor) /m _(vapor)/(m _(vapor) +m _(liquid))

where m_(vapor) is the mass flow rate of vapor in the tube, m_(liquid)is the mass flow rate of liquid in the tube, and m is the total massflow rate in the tube (m=m_(vapor)+m_(liquid)). The mass flow rate ofliquid is defined as:

m _(liquid)=ρ_(liquid)*ν_(liquid) *A _(liquid)

where ρ_(liquid) is the density of the liquid, and A_(liquid) is thecross-sectional area occupied by liquid at point x in the tube.Similarly, the mass flow rate of vapor is defined as:

m _(vapor)=ρ_(vapor)*ν_(vapor) *A _(vapor)

where ρ_(vapor) is the density of the vapor. The distribution of vaporin a two-phase flow of coolant 50, such as a two-phase flow of coolantwithin a heat sink module 100 mounted on a heat-generating surface 12,affects both the heat transfer properties and the flow properties of thecoolant 50. These properties are discussed in greater detail below.

A number of flow patterns or “flow regimes” have been observedexperimentally by viewing flows of two-phase liquid-vapor mixturespassing through transparent tubes. While the number and characteristicsof specific flow regimes are somewhat subjective, four principal flowregimes are almost universally accepted. These flow regimes are shown inFIG. 58 and include (1) bubbly flow, (2) slug flow, (3) churn flow, and(4) annular flow. FIG. 58( a) shows bubbly flow having a first numberdensity of bubbles, and FIG. 58( b) shows bubbly flow having a secondnumber density of bubbles where the second number density is greaterthan the first number density of FIG. 58( a). FIG. 58( c) shows slugflow. FIG. 58( d) shows churn or churn-turbulent flow. FIG. 58( e) showsannular flow. Beyond annular flow, the flow will transition throughwispy-annular flow before eventually reaching single-phase vapor flow.

Bubbly flow is generally characterized as individually dispersed bubbles275 transported in a continuous liquid phase. Slug flow is generallycharacterized as large bullet-shaped bubbles separated by liquid plugs.Churn flow is generally characterized as vapor flowing in a chaoticmanner through liquid, where the vapor is generally concentrated nearthe center of the tube, and the liquid is displaced toward the wall ofthe tube. Annular flow is generally characterized as vapor forming acontinuous core down the center of the tube and a liquid film flowingalong the wall of the tube.

To predict an existence of a particular flow regime, or a transitionfrom one flow regime to another, requires the above-mentioned visuallyobserved flow regimes to be quantified in terms of measurable (orcomputed) quantities. This is normally accomplished through the use of aflow regime map. An example of a flow regime map is provided in FIG.59A. The flow regime map shown in FIG. 59A is valid for steam-watersystems and shows ρ_(vapor)*j_(vapor) ² on the x-axis andρ_(vapor)*j_(vapor) ² on the y-axis. A similar flow regime map cancreated for a dielectric coolant 50, such as a hydrofluorocarboncoolant, flowing over a heat-generating surface 12 within a heat sinkmodule 100 or flowing within a flexible section of tubing 225, asdescribed herein.

FIG. 59B shows the four two-phase flow regimes, including bubbly flow,slug flow, churn flow, and annular flow, plotted on void fraction versusmass flux axes. To maintain stability within the cooling apparatusduring operation, it can be desirable to maintain either single-phaseliquid flow, bubbly flow, or a combination thereof throughout theapparatus. Experimental testing confirmed that bubbly flow does notresult in flow instabilities within the cooling apparatus 1. Conversely,the presence of slug, churn, or annular flow can result in flowinstabilities and should therefore be avoided. To remain comfortablywithin the bubbly flow regime, it can be desirable to maintain thecoolant below a predetermined void fraction and/or above a predeterminedmass flux. The desired predetermined void fraction and predeterminedmass flux can depend on several factors, including the configuration ofthe cooling apparatus 1 (e.g. components and layout), the type ofcoolant 50 being used, the coolant pressure within the apparatus, andthe temperature of the surface to be cooled 12. In some examples, thevoid fraction of the coolant can be about 0-0.5, 0-0.4, 0-0.3, 0-0.2, or0-0.1. In some examples, the mass flux of the coolant flowing through aheat sink module 100 can be about 10-2,000, 500-1,000, 750-1,500,1,000-2,500, 2,250-2,500, 2,000-2,700, or greater than 2,700 kg/m2-s. Asshown in FIG. 59B, as the void fraction increases (e.g. from about0.3-0.5), the mass flux of the coolant must also increase to avoidtransitioning from bubbly flow to slug or churn flow.

FIG. 60 shows a flow boiling curve where heat transfer rate is plottedas a function of “excess temperature” (T_(e)). Excess temperature is thedifference between the actual temperature of the surface to be cooled 12and the fluid saturation temperature (T_(e)=T_(surface)−T_(sat)). Thecurve is divided into 5 regions (a, b, c, d, and e), each correspondingto certain heat transfer mechanisms.

In region (a) of FIG. 60, a minimum criterion for boiling is that thetemperature of the heat-generating surface 12 exceeds the localsaturation temperature of the coolant (T_(sat)). In other words, somedegree of excess temperature (T_(e)) is required for boiling to occur.In region (a), the excess temperature may be insufficient to supportbubble formation and growth. Therefore, heat transfer may occurprimarily by single-phase convection in region (a).

In region (b) of FIG. 60, bubbles begin forming at nucleation sites onthe heat-generating surface 12. These nucleation sites are generallyassociated with crevices or pits on the heat-generating surface 12 inwhich non-dissolved gas or vapor accumulates and results in bubbleformation. As the bubbles grow and depart from the surface 12, theycarry latent heat away from the surface and produce turbulence andmixing that increases the heat transfer rate. Boiling under theseconditions is referred to as nucleate boiling. In region (b), heattransfer is a complicated mixture of single-phase forced convection andnucleate boiling. This region is often called the mixed boiling or“partial nucleate boiling region.” As the temperature of theheat-generating surface 12 increases, the percentage of surface areathat is subject to nucleate boiling also increases until bubbleformation occupies the entire heat-generating surface 12.

In region (c) of FIG. 60, bubble density increases rapidly as thesurface temperature increases further beyond the saturation temperature(T_(sat)). In this region, heat transfer can be dominated by bubblegrowth and departure from the surface 12. Formation and departure ofthese bubbles 275 can transport large amounts of latent heat away fromthe surface 12 and greatly increase fluid turbulence and mixing in thevicinity of the heat-generating surface 12. As a result, heat transfercan become independent of bulk fluid conditions such as flow velocityand temperature. Heat transfer in this region is know as “fullydeveloped nucleate boiling” and is characterized by a substantialincrease in heat transfer rate in response to only moderate increases insurface 12 temperature. However, there is a limit to the maximum rate ofheat transfer that is attainable with fully developed nucleate boiling.At some point, the bubble density at the heat generating surface 12cannot be increased any further. This point is know as the critical heatflux (“CHF”) and is denoted as c* in FIG. 60. One theory is that atpoint c*, the bubble density becomes so high that the bubbles actuallyimpede the flow of liquid back to the surface 12, since bubbles in closeproximity tend to coalesce, forming insulating vapor patches thateffectively block the liquid coolant from reaching the heat-generatingsurface 12 and thereby prevent the liquid coolant from extracting latentheat, for example, by undergoing a phase change (i.e. boiling) at thesurface 12.

It may be possible to delay the onset of critical heat flux by employingthe cooling apparatuses 1 and methods described herein (e.g. heat sinkmodules capable of providing jet stream 16 impingement) that increasethe heat transfer rate from the heated surface 12, thereby allowing thecooling apparatus 1 to safely and effectively cool a heat generatingsurface 12 that is at a temperature well above the saturationtemperature of the coolant (e.g. about 20-30 deg C. above T_(sat))without reaching or exceeding critical heat flux. In some examples,delaying the onset of critical heat flux, and thereby increasing theheat transfer rate of the cooling apparatus 1 to previously unattainablerates, can be achieved by increasing the three-phase contact line 58length, as described herein (see e.g. FIG. 63 and related description),by using the methods and components (e.g. heat sink modules 100)described herein, which can provide a plurality of jet stream 16impinging against a heated surface 12 where the jets are positioned at apredetermined jet height 18 away from the heated surface 12. To delaythe onset of critical heat flux (and thereby allow the cooling apparatus1 to operate safely and effectively in region (c) shown in FIG. 60), amass flow rate 51, jet height 18, orifice 155 diameter, coolanttemperature, and coolant pressure can be selected from the rangesdescribed herein to provide a plurality of jet streams 16 that impingethe surface to be cooled 12 and effectively increase the three-phasecontact line 58 length proximate the surface to be cooled 12. Althoughthe cooling apparatus 1 can operate extremely well in regions (a) and(b), the efficiency of the cooling apparatus 1 may be highest whenoperating in region (c).

As the temperature of the surface 12 increases beyond the temperatureassociated with critical heat flux, the heat transfer rate actuallybegins to decrease, as shown in region (d) of FIG. 60. Further increasesin the surface 12 temperature simply result in a higher percentage ofthe surface 12 being covered by insulating vapor patches. Theseinsulating vapor patches reduce the area available for liquid to vaporphase change (i.e. boiling). Therefore, despite the surface temperature(T_(surface)) continuing to increase, the overall heat transfer rateactually decreases, as shown in region (d) of FIG. 60. This region isreferred to as the partial film or “transition film boiling region.”Reaching or exceeding the temperature associated with critical heat fluxcan be undesirable, since performance can decrease and becomeunpredictable. Moreover, due to rapid production of vapor proximate thesurface to be cooled 12, the two-phase flow in the cooling apparatus 1can increase in quality and transition from bubbly flow to slug, churn,or annular flow, which can result in undesirable pressure surges withinthe system due to a volume fraction of vapor exceeding a stable workingrange. It is therefore desirable to operate in regions (a), (b), or (c),below the onset of critical heat flux at point c*.

In region (e) of FIG. 84, a vapor layer covers the heat-generatingsurface 12. In this region, heat transfer occurs by conduction andconvection through the vapor layer with evaporation occurring at theinterface between the vapor layer and the liquid coolant. This region isknown as the “stable film boiling region.” Similar to region (d), region(e) is not suitable for stable operation of the cooling apparatus 1 dueto significant vapor formation resulting in slug, churn, or annularflow.

FIG. 61 shows a flow boiling curve for water at 1 atm, where heat fluxis plotted as a function of excess temperature. As noted above, excesstemperature is the difference between the actual temperature of thesurface to be cooled 12 and the fluid saturation temperature(T_(e)=T_(surface)−T_(sat)). The curve of FIG. 61 shows the onset ofnucleate boiling, the point of critical heat flux, and the Leidenfrostpoint. Between the critical heat flux point and the Leidenfrost point isa transition boiling region where the coolant vaporizes almostimmediately on contact with the heated surface 12. The resulting vaporsuspends the liquid coolant on a layer of vapor within the outletchamber 150 and prevents any further direct contact between the liquidcoolant and the heated surface 12. Since vapor coolant has a much lowerthermal conductivity than liquid coolant, further heat transfer betweenthe heated surface 12 and the liquid coolant is slowed downdramatically, as shown by the downward slope of the plot between CHF andthe Leidenfrost point. Beyond the Leidenfrost point, radiation effectsbecome significant, as radiation from the heated surface 12 transfersheat through the vapor layer to the liquid coolant suspended above thevapor layer, and the heat flux again increases.

Experimental Data

FIG. 8 shows a plot of experimental data showing power consumed versustime to cool a computer room 425 having forty active dual-processorservers 400. The left portion of the plot, extending from about 15 to390 minutes, shows power consumed by a CRAC tasked with cooling thecomputer room 425. From about 15 to 190 minutes, the servers 400 werefully utilized, and from about 240 to 360 minutes, the servers were atidle state. At about 390 minutes, the cooling apparatus 1 was activatedto assist the CRAC with cooling the servers 400. However, the heat sinkmodules 100 connected to the cooling apparatus 1 were only installed onmicroprocessors in 25% of the servers (ten of forty servers).Nevertheless, a dramatic reduction in power consumption was recorded.From 390 to 590 minutes, the cooling apparatus 1 conserved about 1.5 kWof power compared to the baseline idle state cooled by the CRAC only,and from about 625 to 840 minutes, the cooling apparatus 1 conservedabout 2 kW of power compared to the baseline fully utilized state cooledby the CRAC only. The reduction in power consumption measured in thisexperiment is expected to scale as more servers in the computer room areconnected to the cooling apparatus 1. Consequently, if heat sink modulesof the cooling apparatus 1 were installed on microprocessors of allforty servers, reductions in power consumption of about 6 kW (i.e. 55%)and 8 kW (i.e. 67%) compared to the baseline idle and baseline fullyutilized states, respectively, are expected. Reductions in powerconsumption of this magnitude can translate to significant savings inannual operating expenses for computer room and data center operators.

Experimental tests have demonstrated that significantly higher heattransfer rates are achievable with the cooling apparatus 1 than withexisting single-phase pumped liquid systems. This higher heat transferrate can be attributed, at least in part, to establishing conditions inan outlet chamber 150 of the heat sink module 100 that promote boilingof the coolant proximate the surface to be cooled 12. Experimental testshave confirmed that the heat sink module 100 shown in FIG. 21 is capableof dissipating a heat load of about 500 thermal watts, and the redundantheat sink module 700 shown in FIG. 51A is capable of dissipating a heatload of about 800 thermal watts.

During testing, a heat sink module 100 was provided that contained aplurality of orifices 155 configured to provide impinging jets streams16 of coolant 50 directed against a surface to be cooled 12, as shown inFIG. 26. In a first test, the pressure in the outlet chamber 150 of theheat sink module 100 was set to establish a saturation temperature ofabout 95° C. for the coolant. In a second test, the pressure in theoutlet chamber 150 of the heat sink module 100 was set to establish asaturation temperature of about 74° C. for the coolant. The saturationtemperature of about 74° C. was chosen to substantially match the meantemperature of the heated surface (i.e. surface to be cooled 12) in thetest. The same flow rate of coolant was used for each test. During thesecond test, bubbles 275 were generated in the outlet chamber 150 withthe coolant having the lower saturation temperature. Such a phase changedid not occur in the outlet chamber 150 with coolant having the highersaturation temperature in the first test. Overall, the heat transferperformance increased by 80% with the lower saturation temperature (i.e.the second test) where bubbles were generated compared to the highersaturation temperature (i.e. the first test) where bubbles were notgenerated.

One benefit of the cooling technology described herein is the ability toefficiently cool local hot spots on a heat-generating device 12 (e.g.hot spots on microprocessors 415). For example, if just one core of agiven microprocessor 415 is more heavily utilized than other cores inthe same processor, and a plurality of jet streams of coolant aredirected at the surface of the microprocessor, more evaporation willoccur proximate the hot core, thereby increasing the local heat transferrate proximate the hot core relative to the cooler cores, and therebyself-regulating to maintain the entire surface 12 of the microprocessorat a more uniform temperature than is possible with purely single-phasecooling systems that are incapable of self-regulating. Because thecooling apparatus 1 is capable of self-regulating to cool local hotspots (e.g. by providing local increases in heat transfer rates throughevaporation), the entire cooling system can be operated at lower flowrate and pressure, which conserves energy, and still handle fluctuationsin processor temperature caused by variations in utilization. This is insharp contrast to existing liquid cooling systems that are not capableof self-regulating to cool local hot spots and must therefore beoperated at much higher flow rates and pressures to ensure adequatecooling of hot spots, for example, on microprocessors. In other words,existing liquid cooling systems must operate continuously at a settingthat is designed to handle a peak heat load to ensure the system iscapable of handling the peak heat load if it occurs. As a result, whenthe microprocessor is not being heavily utilized (which is quite often)existing systems operate at a pressure and flow rate that areconsiderably above where they would otherwise need to operate to handlea non-peak heat load. This approach needlessly consumes a significantamount of excess energy, and is therefore undesirable.

Coolant

As used herein, the general term “coolant” refers to any fluid capableof undergoing a phase change from liquid to vapor or vice versa at ornear the operating temperatures and pressures of the cooling apparatuses1. The term “coolant” can refer to fluid in liquid phase, vapor phase,or mixtures thereof (e.g. two-phase bubbly flow). A variety of coolants50 can be selected for use in the cooling apparatus 1 based on cost,level of optimization desired, desired operating pressure, boilingpoint, and existing safety regulations that govern installation (e.g.such as regulations set forth in ASHRAE Standard 15 relating topermissible quantities of coolant per volume of occupied buildingspace).

Selection of the coolant 50 for the cooling apparatus 1 can beinfluenced by desired dielectric properties of the coolant, a desiredboiling point of the coolant, and compatibility with polymer materialsused to manufacture the heat sink module 100 and the flexible tubing 225of the apparatus 1. For instance, the coolant 50 may be selected toensure little or no permeability through system components (e.g. heatsink modules and flexible tubing) and no damage to any system components(e.g. to ensure that seals are not damaged or compromised by thecoolant).

Water is readily abundant and inexpensive. Although the coolingapparatuses 1 described herein can be configured to operate with wateras the coolant 50, water has certain traits that make it less desirablethan other coolant options. For instance, water does not change phase ata low temperature (such as 40-50° C.) without operating at very lowpressures, which can be difficult to maintain in a relativelyinexpensive cooling apparatus that includes at least some standardfittings and system components (e.g. gear pumps, pressure regulators,valves, and flexible tubing). In addition, water as a coolant requires anumber of additives (e.g. corrosion inhibitors and mold inhibitors) andcan absorb a range of materials from surfaces of system components itcontacts. As water changes phase, these materials can precipitate out ofsolution, causing fouling or other issues within system components.Fouling is undesirable, since it can reduce system performance byeffectively increasing the thermal resistance of certain components thatare tasked with expelling heat from the system (e.g. heat exchanger 40)or tasked with absorbing heat into the system from devices being cooledby the system (e.g. copper base plate 430). The above-mentionedchallenges can be overcome with appropriate filtration and fittings,which adds cost to the system. However, water is a highly effective heattransfer medium, so where increased heat transfer rates are required,the additional cost and complexity associated with using water as thecoolant may be justified.

In some examples, it can be preferable to use a dielectric fluid, suchas a hydrofluorocarbon coolant 50 instead of water. Unlike water,dielectric coolants 50 can be used in direct contact with electricaldevices, such as CPUs, memory modules, and power converters withoutshorting electrical connections of the devices. Therefore, if a leakdevelops in the cooling apparatus and coolant drips onto an electricaldevice, there is no risk of damage to the electrical device. In someexamples of the cooling apparatus 1, the dielectric coolant 50 can bedelivered directly (e.g. by way of one or more jet streams 16) onto oneor more surfaces of the electronic device (e.g. one or more surfaces ofa microprocessor 415), thereby eliminating the need for commonly-usedthermal interface materials (e.g. copper base plates 430 and thermalbonding materials) between the flowing coolant 50 and the electronicdevice and can thereby eliminate thermal resistances associated withthose thermal interface materials, thereby enhancing performance andoverall efficiency of the cooling apparatus 1.

Non-limiting examples of dielectric hydrofluorcarbon coolants 50 include1,1,1,3,3-pentafluoropropane (known as R-245fa), hydrofluoroether (HFE),1-methoxyheptafluoropropane (known as HFE-7000),methoxy-nonafluorobutane (known as HFE-7100). One version of R-245fa iscommercially available as GENETRON 245fa from Honeywell InternationalInc. headquartered in Morristown, N.J. HFE-7000 and HFE-7100 (as well asHFE-7200, HFE-7300, HFE-7500, HFE-7500, and HFE-7600) are commerciallyavailable as NOVEC Engineered Fluids from 3M Company headquartered inMapleton, Minn. FC-40, FC-43, FC-72, FC-84, FC-770, FC-3283, and FC-3284are commercially available as FLUOROINERT Electronic Liquids also from3M Company.

GENETRON 245fa is a pentafluoropropane and has a boiling point of 58.8degrees F. at 1 atm, a molecular weight of 134.0, a critical temperatureof 309.3 degrees F., a critical pressure of 529.5 psia, a saturatedliquid density of 82.7 lb/ft3 at 86 degrees F., a specific heat ofliquid of 0.32 Btu/lb-deg F at 86 degrees F., and a specific heat ofvapor of 0.22 btu/lb-deg F at 1 atm and 86 degrees F. GENETRON 245fa hasa Safety Group Classification of A1 under ANSI/ASHRAE Standard 36-1992.

NOVEC 7000 has a boiling point of 34 degrees C., a molecular weight of200 g/mol, a critical temperature of 165 degrees C., a critical pressureof 2.48 MPa, a vapor pressure of 65 kPa, a heat of vaporization of 142kJ/kg, a liquid density of 1400 kg/m3, a specific heat of 1300 J/kg-K, athermal conductivity of 0.075 W/m-K, and a dielectric strength of about40 kV for a 0.1 inch gap.

NOVEC 7100 has a boiling point of 61 degrees C., a molecular weight of250 g/mol, a critical temperature of 195 degrees C., a critical pressureof 2.23 MPa, a vapor pressure of 27 kPa, a heat of vaporization of 112kJ/kg, a liquid density of 1510 kg/m3, a speceif heat of 1183 J/kg-K, athermal conductivity of 0.069 W/m-K, and a dielectric strength of about40 kV for a 0.1 inch gap.

Novec 649 Engineered Fluid is also available from 3M Company. It is afluoroketone fluid (C₆-fluoroketone) with a low Global Warming Potential(GWP). It has a boiling point of 49 degrees C., a thermal conductivityof 0.059, a molecular weight of 316 g/mol, a critical temperature of 169degrees C., a critical pressure of 1.88 MPa, a vapor pressure of 40 kPa,a heat of vaporization of 88 kJ/kg, a liquid density of 1600 kg/m3.

In some examples, the coolant can be a combination of dielectric fluidsdescribed above. For instance, the coolant can include a combination ofR-245fa and HFE-7000 or a combination of R-245fa and HFE-7100. In oneexample, the coolant 50 can include about 1-5, 1-10, 5-20, 10-20, 15-30,or 25-50 percent R-245fa by volume with the remainder being HFE-7000. Inanother example, the coolant 50 can include about 1-5, 1-10, 5-20,10-20, 15-30, or 25-50 percent R-245fa by volume with the remainderbeing HFE-7100.

Combining dielectric hydrocarbon fluids to form a coolant mixture foruse in the cooling apparatus 1 can be desirable for several reasons.First, certain fluids, such a R-245fa may be regulated in ways thatrestrict the volume of fluid that can be used in an occupied building,such as an office building. Since R-245fa has been shown to perform wellin the cooling apparatus 1, it may be desirable to use as much R-245faas legally permitted in the cooling apparatus 1, and if additionalcoolant volume is required, to use an unregulated coolant, such asHFE-7000 or HFE-7100, to increase the total coolant volume within thecooling apparatus 1 to reach the desired coolant volume.

Second, combining dielectric coolants can allow a coolant mixture with adesired boiling point to be formulated. R-245fa has a boiling point ofabout 15.2 degrees C. at 1 atm, and HFE-7000 has a boiling point ofabout 34 degrees C. at 1 atm. In some examples, neither of these boilingpoints may be optimal for use in a particular application. By combiningR-245fa and HFE-7000, a coolant mixture can be created that behaves asif its boiling point were somewhere between 15.2 and 34 degrees C.,depending on the mixture ratio. The ability to create a coolant mixturewith a specific boiling point can be highly desirable for customtailoring the coolant mixture for a specific application depending onthe anticipated operating temperature of the surface to be cooled 12.

Cooling Apparatus

FIG. 1 shows a front perspective view of a cooling apparatus 1 installedon a plurality of racks 410 of servers 400 in a data center or computerroom 425. The racks 410 of servers 400 are arranged in a row with a pump20, reservoir 200, and other system components arranged near the leftside of the row of racks 410. One or more tubes extend along the lengthof the row of racks 410 and fluidly connect servers 400 within each rack410 to the cooling apparatus 1, thereby allowing heat-generatingcomponents 12 (such as microprocessors) within each server to be cooledby the cooling apparatus 1.

In addition to cooling microprocessors in servers, the cooling apparatuscan be configured to cool a wide variety of other devices. In someexamples, the cooling apparatus 1 can be configured to cool one or moreheat-producing surfaces 12 associated with batteries, electric motors,control systems, power electronics, chemistry equipment (e.g. rotaryevaporators or reflux distillation condensers), or machines ormechanical devices (e.g. turbines, internal combustion engines,radiators, braking components, turbochargers, engine intake manifolds,plasma cutters, drills, oil and gas exploratory and recovery equipment,water jet cutters, welding systems, or computer numerical control (CNC)mills or lathes).

FIG. 2A shows a rear view of the cooling apparatus 1, and FIG. 2B showsa detailed rear view of a right portion of the cooling apparatus shownin FIG. 2A. In this example, the cooling apparatus 1 can include aplurality of components and sub-assemblies fluidly connected to providea cooling apparatus 1 that is capable of locally cooling one or moreheat-producing surfaces 12 (e.g. flat surfaces, curved surfaces, orcomplex surfaces), such as surfaces associated with CPUs, memorymodules, and motherboards located within the server housings.

FIG. 3 shows a left side view of the cooling apparatus 1 of FIG. 1.Portions of a primary cooling loop 300 are visible in FIG. 3, includinga pump 20, reservoir 200, drain/fill location 245, shut-off valve 250,pressure gauge 255, inlet manifold 210, and return line 230. Portions ofa first bypass 305 are also visible in FIG. 3, including a pressureregulator 60 and heat exchanger 40. As shown in FIG. 3, the primarycooling loop 300 and the first bypass 305 can be fluidly connected tothe reservoir 200.

FIGS. 11A-14, 16-20, and 68-72 present a variety of configurations forthe cooling apparatus 1. Depending on its configuration, the coolingapparatus 1 can include a plurality of fluidly connected components,including one or more pumps 20, one or more reservoirs 200, one or moreheat exchangers 40, one or more inlet manifolds 205, one or more outletmanifolds 210, one or more pressure regulators 60, one or more sectionsof flexible tubing 225, and one or more heat sink modules 100 mountedon, or placed in thermal communication with, one or more surfaces to becooled 12.

FIG. 11A shows an exemplary schematic of a cooling apparatus 1 havingone heat sink module 100 mounted on a heat-generating surface 12. Theheat-generating surface 12 can be any surface having a temperature aboveambient temperature that requires cooling. For instance, theheat-generating surface 12 can be a surface of a mechanical orelectrical device, such as a surface of a microprocessor 415. Asidentified by dashed lines in FIG. 11B, the cooling apparatus 1 caninclude a primary cooling loop 300 fluidly connecting a pump 20, atleast one heat sink module 100, a return line 230, and a reservoir 200.The pump 20 can be configured to draw single-phase liquid coolant fromthe reservoir 200 and deliver a flow 51 of pressurized single-phaseliquid coolant 50 to an inlet port 105 of a heat sink module 100. Theheat sink module 100, being mounted on the heat-generating surface 12,can be configured to direct a flow of pressurized coolant 51 at thesurface of the heat-generating surface 12 in the form of a plurality ofjet streams 16 of coolant impinging the heat-generating surface 12,thereby facilitating heat transfer from the heat-generating surface tothe flow of coolant. The return line 230 can be configured to transportthe flow of coolant 51, which may include two-phase bubbly flow, fromthe outlet port 110 of the heat sink module 100 back to the reservoir200 where it can be mixed with single-phase liquid coolant to promotecondensation of vapor bubbles within the two-phase bubbly flow, therebyresulting in transition of the two-phase bubbly flow back tosingle-phase liquid coolant that can once again be delivered to the pump20 without risk of cavitation or vapor lock.

As identified by dashed lines in FIG. 11C, the cooling apparatus 1 caninclude a first bypass 305 including a pressure regulator 60 and a heatexchanger 40. The purpose of the first bypass 305 can be to divert aportion of the flow 51 away from the primary cooling loop 300 andthrough the heat exchanger 40 where the fluid can be further cooled andreturned to the reservoir 200 to assist in condensing vapor in thereservoir by further reducing the bulk fluid temperature of the liquidcoolant in the reservoir 200. As a result, when the two-phase bubblyflow is delivered to the reservoir via the return line, it immediatelymixes in the reservoir with a large volume of coolant that is well belowthe saturation temperature of the liquid, thereby promoting condensationof all vapor bubbles entering the reservoir via the return line. Theportion of flow 51 that is diverted through the first bypass 305 can becontrolled, at least in part, by adjusting the pressure regulator 60located in the first bypass 305. The amount of flow that is divertedthrough the first bypass 305 may depend on the reservoir temperatureand/or the quality (x) of the flow returning to the reservoir via thereturn line 230. For example, if the temperature of the fluid in thereservoir 200 increase to a predetermined threshold value (e.g. about10-15 degrees below the saturation temperature), or if the quality ofthe flow increases (e.g. to about 0.1-0.3), it can be desirable toincrease the amount of flow through the first bypass 305 to remove heatfrom the liquid using the heat exchanger so that cool liquid coolant canbe circulated back to the reservoir 200 to ensure that vapor bubbles 275rapidly condense within the reservoir 200 and are not permitted to reachthe pump 20.

In the schematic shown in FIG. 11A, the heat exchanger 40 is positioneddownstream of the pressure regulator 60, but this is not limiting. Inother examples, the pressure regulator 60 can be positioned downstreamof the heat exchanger 40, as shown in FIG. 12A, where the coolingapparatus 1 has one heat sink module 100 mounted on a heat source 12 anda pressure regulator 60 located downstream of the heat exchanger 40 inthe first bypass 305.

As identified by dashed lines in FIG. 11D, the cooling apparatus 1 caninclude a second bypass 310 including a pressure regulator 60. Thesecond bypass 310 can route a portion of the pressurized single-phaseliquid flow around the heat sink module 100 and can be fluidly connectto the primary cooling loop 300 downstream of the heat sink module 100.Depending on the surface temperature of the heat-generating surface 12and settings of the cooling apparatus (e.g. pressure, flow rate, coolanttype, bulk coolant temperature at the module inlet 105, coolantsaturation temperature, etc.), the primary cooling loop 300 may betransporting two-phase bubbly flow downstream of the outlet port 110 ofthe heat sink module 100. To encourage condensing of bubbles 275 withinthe two-phase bubbly flow before the coolant reaches the reservoir (andthereby reducing the likelihood of vapor being introduced to the pump20), the second bypass 310 can route single-phase liquid coolant aroundthe heat sink module 100 and deliver the single-phase liquid coolant tothe primary cooling loop 300 that is carrying two-phase bubbly flow,effectively mixing the two flows upstream of the reservoir 200. Thismixing encourages condensing of all or a portion of the bubbles in thetwo-phase bubbly flow before the flow is delivered back to the reservoir200 via the return line 230, thereby further reducing the likelihoodthat any bubbles 275 will be drawn from the reservoir 200 and fed to thepump, where they could cause unwanted cavitation.

Because the bubbles 275 formed in the two-phase bubbly flow arerelatively small and are distributed (i.e. dispersed) throughout theliquid coolant 50, the bubbles are carried through the primary coolingloop 300 by the momentum of the liquid coolant and do not travelvertically within the system due to gravitational effects. Consequently,the cooling apparatus 1 does not require a condenser mounted at a highpoint in the system to collect and condense vapor bubbles back toliquid, as competing systems do. Since no condenser is required, thecooling apparatus 1 can be much smaller in size and less expensive thancompeting systems that require a condenser. Also, the heat sink modules100 and sections of flexible tubing 225 described herein can beinstalled in any orientation without concerns of vapor lock. To thecontrary, in competing systems, the orientation of system components canbe critical to ensure that all vapor is transported to a condenserlocated at a high point in the system by way of gravity to ensure thatvapor does not make its way to the pump, where it could result in vaporlock and/or pump cavitation and system failure.

As used herein, “fluid communication” between two or more elementsrefers to a configuration in which fluid can be communicated between oramong the elements and does not preclude the possibility of having afilter, flow meter, temperature or pressure sensor, or other devicesdisposed between such elements. The elements comprising the coolingapparatus 1 are preferably configured in a closed fluidic system, asshown in FIG. 11A, thereby permitting containment of the coolant 50which would otherwise be prone to evaporate into the environment.

Pressure Regulator

The pressure regulator 60 can be any suitable type of pressure regulatorthat is capable of achieving suitable working pressures ranges and flowrates described herein to ensure smooth operation of the coolingapparatus 1. In some examples, the pressure regulator 60 can be a reliefvalve, such as a Series 69 relief valve manufactured by Aquatrol, Inc.of Elburn, Ill. One suitable Series 69 relief valve has an adjustmentrange of about 0-15 psi and a maximum flow rate of about 6.9 gallons perminute. This model pressure regulator is suitable for a coolingapparatus 1 configured to cool several racks 410 of servers 400 as shownin FIG. 3. For applications where a larger or smaller cooling apparatus1 is required, a larger or smaller model pressure regulator can be used.

As shown in FIG. 11A, the pressure regulator 60 can be located in thesecond bypass 310 of the cooling apparatus 1 and can be used to controlthe pressure differential between the inlet port 105 and the outlet port110 of the heat sink module (i.e. the pressure differential between thehigh-pressure coolant 54 at the inlet port 105 and the low-pressurecoolant 55 at the outlet port 110). Where the cooling apparatus 1 has aplurality of heat sink modules 100 fluidly connected in parallel to theinlet manifold 210 and outlet manifold 215, as shown in FIG. 16, thepressure regulator 60 can be used to control the pressure differentialbetween the inlet manifold and the outlet manifold.

In the cooling apparatus 1 shown in FIG. 11A, by adjusting the pressureregulator 60 located in the second bypass 310, the pressure differentialbetween the inlet port 105 and outlet port 110 can be controlled. In thecooling apparatus 1 shown in FIG. 16, the pressure regulator 60 can beadjusted to provide a pressure differential between the inlet manifold210 and the outlet manifold 215. In one example, the pressure regulator60 can be adjusted to provide a pressure differential of about 5-15 or10-15 psi between the inlet manifold 210 and the outlet manifold 215.For instance, if the high-pressure coolant 54 in the inlet manifold 210is at a pressure of about 60 psi, the pressure regulator 60 can beadjusted to maintain low-pressure coolant 55 in the outlet manifold 215at a pressure of about 45-55 or 45-50 psi. In another example, if thehigh-pressure coolant 54 in the inlet manifold 210 is at a pressure ofabout 30 psi, the pressure regulator 60 can be adjusted to maintainlow-pressure coolant 55 in the outlet manifold 215 at a pressure ofabout 15-25 or 15-20 psi. In yet another example (where the contents ofthe cooling apparatus 1 are evacuated using a vacuum pump prior toadding the coolant, such that the resting pressure of the coolant isbelow atmospheric pressure), if the high-pressure coolant 54 in theinlet manifold 210 is at a pressure of about 15 psi, the pressureregulator 60 can be adjusted to maintain low-pressure coolant 55 in theoutlet manifold 215 at a pressure of about 0-10 or 0-5 psi.

The pressure regulator 60 located in the second bypass 310 of thecooling apparatus 1, as shown in FIG. 16, can be adjusted to control thecoolant flow rate through the second bypass 310, and by doing so, cansimultaneously adjust the coolant flow rate through the heat sinkmodules 100. For instance, as the pressure differential between theinlet manifold 210 and the outlet manifold 215 shown in FIG. 16 isdecreased by adjusting the pressure regulator 60 located in the secondbypass 310, a higher percentage of coolant flow 51 will pass through thepressure regulator 60, effectively bypassing the heat sink modules 100and resulting in a reduced coolant flow rate through the heat sinkmodules. Conversely, as the pressure differential between the inletmanifold 210 and outlet manifold 215 is increased by adjusting thepressure regulator 60 located in the second bypass 310, a lowerpercentage of coolant flow 51 will pass through the pressure regulator60, resulting in an increased coolant flow rate through the heat sinkmodules 100.

As shown in FIG. 16, the pressure regulator 60 can be arranged inparallel with a plurality of cooling lines. Coolant flow through thepressure regulator 60 and the cooling lines can be similar to the waycurrent flows in a circuit with resistors arranged in parallel.Increasing the flow resistance of the regulator 60 will decrease theflow through the second bypass 310 and increase the flow rate throughthe cooling lines. Conversely, decreasing the flow resistance of theregulator 60 will increase the flow through the second bypass 310 anddecrease the flow rate through the cooling lines.

In some examples, the quality (x) of the two-phase bubbly flow exitingthe heat sink module(s) 100 can be monitored with a sensor. When thequality (x) reaches a predetermined threshold value (e.g. about 0.25),the flow resistance of the pressure regulator 60 in the second bypass310 can be increased to reduce the flow rate through the pressureregulator and increase the flow rate through the heat sink module(s),thereby reducing the quality (x) of the flow exiting the heat sinkmodule(s) to ensure the bubbly-flow does not transition to slug flow orchurn flow (see FIG. 59B) within the flexible tubing 225, which couldresult in flow instability.

Pump

The pump 20 can be any pump capable of generating a positive coolantpressure that forces coolant 50 to circulate through the coolingapparatus 1. In some examples, the pump 20 can generate a positivecoolant pressure that forces coolant through the primary cooling loop300, into an inlet port of a heat sink module 100, and through aplurality of orifices 155 within the heat sink module, therebytransforming the flow of coolant into a plurality of jet streams 16 ofcoolant that impinge against the surface to be cooled 12, as shown inFIG. 26. In some examples, it can be desirable to select a pump 20 thatis capable of pumping single-phase liquid coolant and increasing thepressure of the coolant to about 15-30, 25-45, 30-50, 40-65, 50-75,60-85, 75-150, 5-200, 5-150, or 100-200 psi.

In some examples, the contents of the cooling apparatus 1 may beevacuated using a vacuum pump prior to adding the coolant 50, therebyresulting in a sub-atmospheric pressure within the cooling apparatus 1.The coolant may be added to the system from a container that is also ata sub-atmospheric pressure. Once inside the system, the coolant willremain at a sub-atmospheric pressure. When the pump 20 is activated, itcan be capable of pumping single-phase liquid coolant and increasing thepressure of the coolant to about 5-20, 10-25, or 15-30 psi at the pumpoutlet 22. In this example, the coolant 50 may be HFE-7000, HFE-7100,R-245fa, or a mixture thereof. In one example, the coolant mixture caninclude about 60-95, 70-95, or 85-95% HFE-7000 by volume and theremainder can be R-245fa. In some examples, the pump pressure can be setat a suitable value to provide a flow rate of about 0.7-1.3, 0.8-1.2, or0.9-1.1 liters per minute through each heat sink module 100 in thecooling apparatus 1.

In one example, the pump 20 can be a variable speed positivedisplacement pump, such as a MICROPUMP gear pump by Cole-Parmer ofVernon Hills, Ill. In another example, where the cooling apparatus 1 isdesigned to cool several racks 410 of servers 400, as shown in FIGS.1-3, the pump 20 can be a 1.5 HP vertical, multistage, in-line,centrifugal pump, such as a Model No. A96084444P115030745 from Grundfosheadquartered in Denmark, and in a similar redundant configuration,shown in FIGS. 9 and 10, the cooling apparatus 1 can have two of thesepumps 20 operating independent.

Although a constant speed pump 20 can be used for simplicity, a variablespeed pump can provide greater flexibility for cooling dynamic heatloads, such as microprocessors 415 with varying utilization rates andtemperatures, since the variable speed pump can enable the flow 51 ofcoolant 50 to be adjusted to meet a flow rate required to cool theestimated (e.g. theoretical) or actual (e.g. measured) heat load at theone or more surfaces to be cooled 12, and then adjusted in real-time ifthe heat load is greater or less than the estimated heat load. Morespecifically, increasing the flow rate of coolant 50 may be requiredwhere the heat load is greater than the estimated heat load to avoidreaching critical heat flux at the surface to be cooled 12. Alternately,decreasing the flow rate of coolant 50 may be required where the heatload is less than the estimated heat load to reduce unnecessary powerconsumption by the pump 20. The variable speed pump can be controlled byan electronic control system of the cooling apparatus 1.

In some examples, a pressurizer can be used in place of or in additionto the pump 20. The pressurizer can be pressurized by any suitablemethod or device, such as a pneumatic or hydraulic device that covertsmechanical motion to fluid pressure to provide a volume of pressurizedcoolant within the pressurizer that is then used to circulate coolant 50through the cooling apparatus 1.

Reservoir

In the cooling system 1, the pump 20 can be in fluid communication witha coolant reservoir 200. In some examples, the reservoir 200 can be ametal tank, such as a steel or aluminum tank (see, e.g. FIG. 3), or aplastic tank with a suitable pressure rating. In other examples, thereservoir 200 can be any suitable vessel that is capable of receiving avolume of coolant and safely housing the volume of coolant in compliancewith any governing regulations. As described herein, with respect tocertain embodiments of the cooling apparatus 1, such as embodimentsshown in FIGS. 11A-D, the reservoir 200 can be configured to receive avariety of fluid flows, including two-phase bubbly flow via a primarycooling loop 300 and single-phase liquid flow via a first bypass loop305. However, despite receiving two-phase bubbly flow via the returnline 230 of the primary cooling loop 300, the cooling apparatus 1 can beconfigured to provide exclusively single-phase liquid coolant from areservoir outlet to an inlet 21 of the pump 20. As vapor bubbles 275 areintroduced to the reservoir by bubbly flow from the return line 230, thebubbles 275 tend to migrate to the top of the reservoir 200, andsingle-phase liquid tends to settle in the lower portion of thereservoir due to gravitational effects. A section of tubing 220, such asrigid or flexible section of tubing, can connect the reservoir 200 tothe inlet 21 of the pump 20. In some examples, the section of tubing 220can connect to a reservoir outlet located along a lower portion of thereservoir 200, and preferably at or near a bottom portion of thereservoir, to ensure that only single-phase liquid coolant, and nottwo-phase coolant, is drawn from the reservoir and provided to the inlet21 of the pump 22. Providing only single-phase liquid coolant to thepump 20 can ensure that cavitation within the pump is avoided.Cavitation can occur if two-phase flow is provided to the pump, and isundesirable, since it can damage pump components, resulting indiminished pump capacity or pump failure.

To ensure that only single-phase liquid coolant is provided to the pump20, and thereby avoiding pump cavitation, the volume of coolant in thereservoir 200 can be selected to be a certain volume ratio of the totalvolume of coolant in the cooling apparatus 1. Increasing the volumeratio can increase the likelihood that any vapor bubbles 275 within thetwo-phase bubbly flow being delivered to the reservoir 200 from the oneor more heat sink modules 100 will have an opportunity to condense backto liquid before that quantity of coolant is drawn from the reservoir200 and delivered back to the pump inlet 21 for recirculation throughthe cooling apparatus 1. The preferred volume ratio can depend on avariety of factors, including, for example, the heat load associatedwith the surface being cooled 12, the properties of the coolant 50 beingused, the flow rate of coolant in the system, the flow quality (x) ofcoolant being returned to the reservoir 200, the percentage of coolantflow 51 being diverted through the first and second bypasses (305, 310),the operating pressure of the coolant, and the performance of the heatexchanger 40. In some examples, the volume ratio can be about 0.2-0.5,0.4-1.0, 0.6-1.5, 1.0-2.0, or greater than 2.0. It can be desirable toencourage condensing of any bubbles that may be delivered to thereservoir 200 as two-phase bubbly flow returning from the one or moreheat sink modules 100. Experiments have shown that maintaining thereservoir 200 at a fill level of about 30-90%, 40-80%, or 50-70%, (wherefill level is defined as the percent volume of the reservoir 200occupied by liquid coolant 50) results in effective condensing ofbubbles 275 that are delivered to the reservoir by the return line 230.A liquid-vapor interface is established at the fill level of thereservoir 200, and this liquid-vapor interface may encouragecondensation of the bubbles 275 due to hydrodynamic effects acting onthe two-phase bubbly flow as it is delivered to (e.g. poured or sprayedinto) the reservoir 200 and passes through the liquid-vapor interfacewithin the reservoir and mixes with the sub-cooled single-phase liquidcoolant residing in the reservoir. As shown in FIG. 3, the return line230 carrying the two-phase bubbly flow can deliver the two-phase bubblyflow near an upper portion of the reservoir 200. In some examples, thedelivery point of two-phase bubbly flow to the reservoir 200 can belocated above the fill level of the reservoir to ensure the two-phasebubbly flow is delivered into the head space (i.e. vapor region) of thereservoir, such that gravity draws the two-phase bubbly flow downwardthrough the liquid-vapor interface.

In some examples, the reservoir 200 can include a baffle positioned inthe head space of the reservoir or partially in the head space andpartially below the fill level (i.e. passing through the liquid-vaporinterface). The baffle can be configured to encourage condensing ofbubbles 275 in two-phase bubbly flow delivered to the reservoir 200. Thebaffle can span all or a portion of the reservoir 200 and can bepositioned horizontally, vertically, or obliquely within the reservoir.The baffle can be made of a thermally conductive material, such assteel, aluminum, or copper. When two-phase bubbly flow 51 is deliveredto the reservoir 200, the flow can pass through openings (e.g. aplurality of slots or holes) in the baffle, and heat can transfer fromthe two-phase bubbly flow to the baffle and, in some cases, to the wallsof the reservoir 200 to which the baffle is mounted or in contact with.As heat is transferred away from the two-phase bubbly flow, bubbles 275within the coolant 50 can condense, either due to decreases in the bulkfluid temperature in the reservoir or due to local decreases in fluidtemperature proximate the condensing bubbles. The openings in the bafflecan have any suitable shape. Non-limiting examples of baffle openingshapes include triangular, round, oval, rectangular, or hexagonal, orpolygonal.

Inlet and Outlet Manifolds

As shown in FIG. 12T, an inlet manifold 210 can receive coolant 50 andcan deliver the coolant to one or more portions of flexible tubing 225that deliver the coolant to one or more heat sink modules 100 fluidlyconnected between the inlet manifold 210 and an outlet manifold 215. Theinlet manifold 210 can have an inner volume that serves as an in-linereservoir for the coolant and effectively dampens pressure pulsations inthe flow 51 of coolant that may be transmitted from the pump 20. In someexamples, the proper size of the inner volume of the inlet manifold 210can be determined by the flow rate of coolant 50 through the inletmanifold. For instance, the inner volume of the inlet manifold 210 maybe configured to hold a volume of coolant that is greater than or equalto a volume equivalent to at least 5 seconds of coolant flow through themanifold. So for a coolant flow rate of about 1 liter/minute, the inletmanifold 210 can have an inner volume of about 0.083 liters. Forsmoother operation, and greater damping of pressure pulsations, theinlet manifold 210 can have an inner volume capable of storing at least10, 15, 20 or more seconds of coolant flow 51. The outlet manifold 215can be configured to have a similar internal volume as the inletmanifold 210 to provide similar damping of pressure pulsations betweenthe heat sink modules 100 and the return line 230.

FIG. 12T shows a schematic of a cooling apparatus 1 configured to cooltwo racks 410 of servers 400. The cooling apparatus 1 in FIG. 12T has asimilar configuration as the cooling apparatus 1 shown in FIGS. 1-3, butthe cooling apparatus 1 in FIG. 12T only shows two server racks 410,whereas the cooling apparatus in FIGS. 1-3 shows eight server racks 410.Also, the cooling apparatus 1 in FIG. 12T shows fewer parallel coolinglines extending between each inlet and outlet manifold (210, 215).Nevertheless, the overall concept is similar. The cooling apparatus 1 inFIG. 12T includes a dedicated inlet manifold 210 and outlet manifold 215for each server rack 410. This configuration provides a modular coolingsystem 1 that can be increased in size to accommodate additional serverracks 410, for example, as a data center 425 increases its server count.Therefore, the configuration in FIG. 12T can easily be modified toresemble the configuration shown in FIGS. 1-3 by adding six additionalserver racks 410 and by increasing the number of cooling lines extendingbetween each inlet and outlet manifold (210, 215).

FIG. 4 shows a rear side view of a server rack 410 with an inletmanifold 210 and outlet manifold 215 mounted vertically to the serverrack 410. The inlet manifold 210 and the outlet manifold 215 can befitted with a plurality of fittings 235, such as quick-connect fittings,that permit individual cooling loops 300 to be hot swapped withoutinterrupting coolant flow through other cooling loops 300 of theapparatus 1. As shown in FIG. 4, the inlet and outlet manifolds (210,215) can each include a plurality of fittings to permit a plurality ofcooling lines 300 to be connected to each manifold. In some examples,the inlet and outlet manifolds (210, 215) can include extra, unutilizedfittings 235, as shown in FIG. 4, to permit future expansion of thenumber of servers 400 cooled by the cooling apparatus 1.

Although the inlet and outlet manifolds (210, 215) are shown in avertical orientation in FIG. 4, this is not limiting. As discussedherein, because the vapor bubbles 275 within the two-phase bubbly floware effectively dispersed and suspended in the coolant flow and do notseek a high point in the cooling apparatus 1 in response togravitational effects, the system components (such as the outletmanifold 215) do not need to be vertically oriented to ensure collectionof vapor, as competing systems do. Consequently, the outlet manifold 215can be oriented horizontally or at any other suitable orientation thatis preferable for a particular installation in view of space constraintsand manifold size.

Flexible Tubing

FIG. 5 shows a top perspective view of a server 400 with its lid removedand a portion of a cooling apparatus 1 having a primary cooling loop 300installed within the server housing. The cooling loop 300 includes twoheat sink modules 100 mounted on vertically oriented heat-generatingcomponents (e.g. CPUs) within the server 400. The heat sink modules 100are arranged in a series configuration and are fluidly connected withsections of flexible tubing 225 to transport coolant between neighboringheat sink modules, from an outlet port 105 of the first heat sink module100 to an inlet port 105 of the second heat sink module. In someexamples, others types of tubing can be used, such as smooth tubing 225,as shown in FIG. 4. More specifically, smooth nylon or fluorinatedethylene propylene (FEP) tubing 225 can be used. In some examples, theflexible tubing 225 can be FEP tubing from Cole-Parmer of Vernon Hills,Ill. and can have a maximum temperature rating of about 400 degrees F.,an inner diameter of about 0.25-0.375 inches, and a maximum workingpressure of about 210 psi. The flexible tubing 225 can be chemicallyinert, nontoxic, heat resistant, and have a low coefficient of friction.In addition, the flexible tubing 225 may not deteriorate with age.

In some applications, corrugated, flexible tubing 225 can providecertain advantages. For instance, corrugated tubing can resist kinkingwhen routed in space-constrained applications, such as within servers400 as shown in FIGS. 5 and 6. Flexible, corrugated tubing can be routedin configurations where the tubing contains bends that result in180-degree directional changes without kinking, as shown in FIG. 6. Insome examples, the flexible, corrugated tubing 225 can be corrugated FEPtubing from Cole-Parmer and can have a maximum temperature rating ofabout 400 degrees F. and a maximum working pressure of about 250 psi.

An advantage of corrugated tubing 225 is that, when transportingtwo-phase bubbly flow, it may delay the onset of slug flow by causingthe breakdown of larger bubbles into smaller bubbles and causing thebreakdown of clusters of bubbles due to frictional effects acting on thebubbles as they pass through the corrugated tubing and contact the innerwalls of the tubing. Slug flow occurs when one or more large orbullet-shaped bubbles of vapor form within the tubing 225. As shown inFIG. 58, large vapor bubbles within slug flow may be nearly as wide asthe inner diameter of the tubing. Slug flow is undesirable, since it cancreate flow instabilities in the cooling apparatus 1, resulting insurging or chugging within the cooling loops 300, making it difficult tomaintain desired pressures in certain components of the cooling system1, such as the heat sink modules 100, and thereby making it difficult toprovide consistent and predictable cooling of a heated surface 12. Slugflow can be combatted by increasing the flow rate through the heat sinkmodules 100 to reduce flow quality (x) (due to less vapor formation),thereby restoring two-phase bubbly flow, for example, betweenseries-connected heat sink modules 100. In some examples, the coolingapparatus 1 can be configured to detect the onset of slug flow (e.g.using a visual flow detection system) at an outlet port 110 of a heatsink module 100 or at some other point in the cooling loop 300 and toautomatically increase the coolant flow rate 51 to restore two-phasebubbly flow at the outlets of the one or more heat sink modules 100.

Another advantage of corrugated tubing 225 is that it can resistcollapse when vacuum pressure is applied to an inner volume of thetubing. Vacuum pressure may be applied to the tubing 225 duringservicing of the cooling apparatus 1. For example, when draining coolant50 from the system 1 to allow for repairs or maintenance to beperformed, vacuum pressure can be applied to a location (e.g. a drain245) in the cooling apparatus 1 to draw out coolant 50 from the tubesand components of the apparatus. Portions of the cooling apparatus 1 canthen be safely disassembled without having to make other arrangementsfor containment of the coolant. Removing coolant 50 through theapplication of vacuum pressure can allow the coolant to be captured in avessel and reused to fill the apparatus when servicing is complete,thereby reducing servicing costs and waste that would otherwise beassociated with discarding and replacing the coolant.

FIG. 6 shows a top view of a server 400 with its lid removed and aportion of a cooling apparatus 1 visible within the server. This exampleof a server 400 includes a motherboard 405, two microprocessors 415, andtwo sets of three memory modules 420. The two microprocessors 415 aremounted parallel to the motherboard 405, and the memory modules 420 aremounted perpendicular to the motherboard 405. The cooling apparatus 1includes two heat sink modules 100 arranged in a series configurationand fluidly connected by flexible sections of flexible tubing 225. Thefirst heat sink module 101 is mounted on a first microprocessor, and thesecond heat sink module 102 is mounted on a second microprocessor. Afirst section of flexible tubing 225 delivers coolant the an inlet port105 of the first heat sink module 101, and a second section of flexibletubing 225 delivers coolant from an outlet port 110 of the first heatsink module 101 to an inlet port 105 of the second heat sink module 102.As, shown, due to its flexibility, the second section of flexible tubing225 can easily be routed around server components for ease ofinstallation. The flexible tubing 225 can be arranged in a variety ofconfigurations, including serpentine configurations, to allow any twoheat sink modules 100 (e.g. within a server housing) to be fluidlyconnected regardless of the orientation or placement of the two heatsink modules.

The heat sink modules 100 can be used within the server 400 to coolelectrical components that produce the most heat, such as themicroprocessors 415. Other components within the server 400 may alsoproduce heat, but the amount of heat produced may not justifyinstallation of additional heat sink modules 100. Instead, to removeheat generated by other electrical devices within the server 400, one ormore fans 26 can be used to expel warm air from the server 400 housing,as shown in FIG. 6. The fans can be configured to draw cool room airinto the server housing 400 and to expel warm air from the housing.

In some examples, the length of a section of flexible tubing 225 betweenseries-connected modules can be at least 4, 6, 12, 18, or 24 inches inlength. In some applications, increasing the length of the section oftubing 225 can promote condensation of bubbles 275 within the bubblyflow between series-connected heat-sink modules due to heat transferfrom the liquid to the tubing 225 and ultimately from the tubing to theambient air, as well as heat transfer within the coolant from the vaporportion of the flow to the liquid portion of the flow, thereby elevatingthe bulk fluid temperature as vapor bubbles collapse. In someapplications, increasing the length of the second section of flexible,corrugated tubing 225 may promote breaking apart of clusters of bubblesthat may form in the two-phase flow, thereby delaying the onset ofplug/slug flow and maintaining two-phase bubbly flow.

Coolant Filter

FIG. 13 shows a schematic of a cooling apparatus 1 including a filter260 located between the reservoir 200 and the pump 20 in the primarycooling loop 300. The filter 260 can trap and prevent debris fromentering and damaging the pump 20. Likewise, the filter 260 can trap andprevent debris from passing through the primary cooling loop 300 to theone or more heat sink modules 100, where the debris could potentiallyclog small orifices 155 in the heat sink modules. The cooling apparatus1 can include one or more filters 260 placed upstream or downstream ofthe pump 20, or in any other suitable locations. The filter 260 can beconnected inline using quick-connect fittings. The filter 260 can be adisposable filter or a reusable filter. The filter can have a micronrating of about 5, 10, or 20 microns.

In some examples, the heat sink module 100 can include a filter 260 toensure that no debris is permitted to enter the heat sink module andclog orifices 155 within the heat sink module. The filter 260 can bedisposed within the heat sink module (e.g. a removable filter that isinserted within the inlet port 105, inlet passage 165, or inlet chamber145), or can be attached in-line with the heat sink module 100, such asa filter component that is threaded onto the inlet port and thatcontains a filtration device. By placing the filter 260 in orimmediately upstream of the heat sink module 100, clogging of orifices155 within the heat sink module can be avoided regardless of wheredebris originates from in the cooling apparatus 1.

Heat Sink Module

The heat sink module 100 can be configured to mount on a surface to becooled 12 and provide a plurality of jet streams 16 (e.g. an array ofjet streams 16) of coolant that impinge against the surface to be cooled12 to effectively remove heat from the surface to be cooled. By removingheat from the surface to be cooled 12, the heat sink module 100 caneffectively maintain the temperature of the surface to be cooled 12 at asuitable level so that a device associated with the surface to be cooled12 is able to operate without overheating (i.e. operate below athreshold temperature).

The heat sink module 100 can include a top surface 160 and a bottomsurface 135 opposite the top surface. The heat sink module 100 can beuniquely sized and shaped for a particular application. For instance,where the heat sink module 100 is tasked with cooling a square-shapedmicroprocessor, the heat sink module 100 can have a square perimeter, asshown in FIGS. 21-24. In this example, the heat sink module 100 can bedefined by a front side surface 175, a rear side surface 180, a leftside surface 185, a right side surface 190, the top surface 160, and thebottom surface 135. In other applications, the perimeter shape of theheat sink module 100 can be round, polygonal, or non-polygonal. In someexamples, the heat sink module 100 can have dimensions that allow it toreplace a traditional finned heat sink. For instance, the heat sinkmodule 100 can have a footprint of about 91.5×91.5 mm or 50×50 mm. Inother examples, the heat sink module can be sized for a specific CPU orGPU. The features of the heat sink module 100 are scalable and can berapidly manufactured using a 3D printing process.

The heat sink module 100 can have any suitable sealing feature locatedon the bottom surface 135 to facilitate sealing against the surface tobe cooled 12 or against an intermediary surface, such as a surface of athermally-conductive base member (e.g. a copper plate 430) that isadhere to the surface to be cooled 12. In some examples, the heat sinkmodule 100 can include a channel 140 along its bottom surface 135, asshown in FIG. 24. The channel 140 can be configured to receive asuitable sealing member 125, such as a gasket or O-ring, as shown inFIG. 23. In some examples, the channel 140 can be a continuous channelthat circumscribes an outlet chamber 150 of the heat sink module 100, asshown in FIG. 24. In other examples, the heat sink module 100 caninclude alternate or additional sealing materials, such as a liquidgasket material, a die cut rubber gasket, an adhesive sealant, or a 3-Dprinted gasket provided on the bottom surface 135 of the heat sinkmodule 100.

Although the bottom surface 135 of the heat sink module shown in FIG. 23is flat, this is non-limiting. For applications involving a contouredsurface to be cooled 12, the bottom surface 135 of the heat sink module100 can have a corresponding contour that matches the contour of thesurface to be cooled 12 and a thereby allows a sealing member 125disposed therebetween to provide a liquid tight seal. In one example,the bottom surface 135 of the heat sink module can have a contourconfigured to match an external surface contour of a cylindrical tube orvessel (e.g. a metallic vessel) used in a chemical process, such as acondensation process or cooling wort in a brewing process. The contouredbottom surface 135 of the heat sink module 100 can allow the heat sinkmodule to be form a liquid-tight seal against the tube or vessel andcool an external surface of the tube or vessel that is exposed withinthe outlet chamber 150 of the heat sink module 100. Where the contentsof a large vessel must be cooled rapidly, such as when chilling wort ina brewing process, a plurality of heat sink modules 100 can be arrangedon the external surface(s) of the large vessel to remove heat from thevessel rapidly, thereby allowing the cooling apparatus 1 to replace aglycol chiller system in a modern brewery or a counterflow chiller(which uses a significant amount of chilled water) in a more traditionalbrewery.

The heat sink module 100 can include mounting holes 130 or locatingholes, as shown in FIGS. 21 and 23, located near corners of the moduleand/or along one or more perimeter portions of the module. Fasteners 115can be inserted through the mounting holes 130, as shown in FIG. 22, andinstalled into threaded holes associated with a mounting surface towhich the heat sink module 100 is mounted, such as a mounting surface ofa thermally conductive base member 430 (e.g. a copper base plate) ordirectly to a mounting surface of an electrical device (e.g. amicroprocessor 415 or a motherboard 405). In some examples, screw-typefasteners 115 can be replaced with alternate types of fastening devicesthat allow for faster installation and/or removal of the heat sinkmodule 100. In one example, the heat sink module 100 can be fastened toa heat source using a buckle mechanism, similar a ski boot buckle, toallow for rapid, tool-less installation. In other examples, the heatsink module 100 can be received by a snap fitting on the surface to becooled 12, thereby allowing the heat sink module to be installed anduninstalled with ease by hand and without tools.

During installation of the heat sink module 100 on a surface to becooled 12, one or more fasteners 115 can be inserted through one or more130 holes in the heat sink module, and the one or more fasteners canengage mounting holes in the surface 12 to permit secure mounting of theheat sink module 100 to the surface 12. As the fasteners 115 aretightened, the heat sink module 100 can be drawn down tightly againstthe surface to be cooled 12, and the sealing member 125 (e.g. o-ring orgasket) can be compressed between the surface and the channel 140. Uponcompression, the sealing member 125 can provide a liquid-tight seal toensure that coolant 50 does not leak from the outlet chamber 150 duringoperation of the cooling system 1 as coolant 50 flows from the inletport 105 to the outlet port 110 of the heat sink module 100.

The heat sink module 100 can include an inlet port 105, as shown in FIG.21. The inlet port 105 can have internal or external threads 170 thatallow a connector 120 to be connected to the inlet port. Any suitableconnector 120 can be used to connect the inlet section of flexibletubing 225 to the inlet port 105. In some examples, as shown in FIG. 22,a metal or polymer connector 120 from Swagelock Company of Solon, Ohiocan be used to connect the flexible tubing to the inlet port 105. Thetop surface 160 of the heat sink module 100 can include visual markings132 to identify a preferred flow direction through the heat sink moduleto ensure proper routing of tubing to and from the heat sink module 100to ensure that coolant flow 51 is delivered to the inlet port 105 andexits from the outlet port 110 and is not accidentally reversed.

As shown in FIG. 25, the heat sink module 100 can include an inletpassage 165 that fluidly connects the inlet port 105 to an inlet chamber145 of the heat sink module. The heat sink module 100 can include adividing member 195 that separates the inlet chamber 145 from the outletchamber 150. The dividing member 195 can have a top surface and a bottomsurface and can include one or more orifices 155 passing from the topsurface to the bottom surface of the dividing member. The orifices 155permit jet streams 16 of coolant 50 to be emitted from the bottomsurface of the dividing member 195 and into the outlet chamber 150 whenpressurized coolant 54 is delivered to the inlet chamber 145, as shownin FIG. 26.

As shown in the cross-sectional view of FIG. 25, the inlet chamber 145can have a geometry that tapers in cross-sectional area from the frontside surface 175 of the heat sink module 100 toward the rear sidesurface 180 of the heat sink module. The tapered cross-sectional area ofthe inlet chamber 145 can ensure that all orifices 155 receive coolant50 at a similar pressure. Similarly, the outlet chamber 150 can increasein cross-sectional area in a direction from the rear surface 180 of theheat sink module toward the front surface 175 of the heat sink module100. The increase in cross-sectional area of the outlet chamber 150 canprovide suitable volume for expansion of the coolant that may occur as aportion of the liquid coolant transitions to vapor, as shown in FIG. 30,and exits the outlet port 110 of the heat sink module 100.

The heat sink module 100 can include one or more inlet passages 165 topermit fluid to enter the inlet chamber 145 and one or more outletpassages 166 to permit fluid to exit the outlet chamber 150. In thismanner, the heat sink module 100 can be configured to permit fluid toflow through the outlet chamber 150. A dividing member 195 can at leastpartially separate the inlet chamber 145 from the outlet chamber 150. Aplurality of orifices 155 can be formed in the dividing member as shownin FIGS. 24 and 25. The plurality of orifices 155 can be configured toeach project a stream 16 of coolant 50 against the surface to be cooled12. In some examples, the streams 16 of fluid projected against thesurface 12 can be jet streams. As used herein, a “jet” or “jet stream”refers to a substantially liquid fluid filament that is projectedthrough a substantially liquid or fluid medium or a mixture thereof. Asused herein, a “jet stream” can include a single-phase liquid fluidfilament or a two-phase bubbly flow filament. “Jet” or “jet stream” iscontrasted with “spray” or “spray stream,” where “spray” or “spraystream” refers to a substantially atomized liquid fluid projectedthrough a substantially vapor medium.

The inlet chamber 145 and the outlet chamber 150 can be formed withinthe heat sink module 100. The heat sink module 100 can be made from anysuitable material and manufactured by any suitable manufacturingprocess. In some examples, the heat sink module 100 can be made of apolymer material and formed through a 3D printing process, such asstereolithography (SLA) using a photo-curable resin. Printers capable ofproducing heat sink modules as shown in FIGS. 21-54 are available from3D Systems, Inc. of Rock Hill, S.C. In other examples, a module body canbe injection molded to reduce cost and manufacturing time and aninsertable orifice plate can be 3-D printed and attached to the modulebody to complete the heat sink module 100.

The heat sink module 100 can be configured to cool a surface 12 of aheat source. The heat sink module 100 can include an inlet chamber 145formed within the heat sink module and an outlet chamber 150 formedwithin the heat sink module. In some examples, the outlet chamber 150can have an open portion along the bottom side surface 135 of the heatsink module 100, as shown in FIG. 23. The open portion of the outletchamber 150 can be enclosed by the surface 12 of a heat source when theheat sink module 100 is installed on the surface 12 of the heat source,as shown in FIG. 26. The heat sink module 100 can include a dividingmember 195 disposed between the inlet chamber 145 and the outlet chamber150. The dividing member 195 can include a first plurality of orifices155 formed in the dividing member. The first plurality of orifices 155can pass from a top side of the dividing member 195 to a bottom side ofthe dividing member and can be configured to deliver a plurality of jetstreams 16 of coolant 50 into the outlet chamber 150 when pressurizedcoolant 54 is provided to the inlet chamber 145, as shown in FIG. 26.

The first plurality of orifices 155 can have any suitable diameter thatallows the orifices to provide well-formed jets streams 16 of coolant 50when pressurized coolant 54 is delivered to the inlet chamber 145 of theheat sink module 100. In some examples, the orifices 155 may all haveuniform diameters, and in other examples, the orifices may not all haveuniform diameters. In either case, the average diameter of the orifices155 can be about 0.001-0.020, 0.001-0.2, 0.001-0.150, 0.001-0.120,0.001-0.005, 0.020-0.045, 0.030-0.050 in, or 0.040 in. An orifice 155diameter of 0.040 in. may be preferable to ensure that orifice cloggingdoes not occur.

In some examples, to ensure that well-formed jet streams 16 of coolant50 are provided by the orifices 155, the length of the orifice can beselected based on the diameter of the orifice. For instance, where thefirst plurality of orifices 155 are defined by a diameter D and anaverage length L, in some cases L divided by D can be greater than orequal to one, about 1-10, 1-8, 1-6, 1-4, 1-3, or 2. In the configurationshown in FIG. 26, the length of each orifice 155 can be determined basedon an angle of the orifice with respect to the surface to be cooled 12and based on the thickness of the dividing member 195. In some examplesthe dividing member 195 can have a thickness of about 0.005-0.25,0.020-0.1, 0.025-0.08, 0.025-0.075, 0.040-0.070, 0.1-0.25, 0.040-0.070,or 0.080 in. The thickness of the dividing member 195 can be selected toprovide a desired length for the orifices 155 to ensure columnar jetstreams 16 of coolant. The thickness of the dividing member can also beselected to ensure structural integrity of the heat sink module 100 whenreceiving pressurized coolant 54 in the inlet chamber 145 and towithstand vacuum pressure when coolant 50 is purged from the coolingsystem 1. To minimize the height of the heat sink module 100 (e.g. toprovide greater freedom when dealing with tight packaging constraints),it can be desirable to select a minimal dividing member thickness thatstill provides well-formed columnar jet streams 16 and adequatestructural integrity.

The heat sink module 100 can be made of any suitable material or process(e.g. a three-dimensional printing process) and can have any suitablecolor or can be colorless. In some examples, it may be desirable tovisually inspect the operation of the heat sink module 100 to ensurethat boiling is occurring within the heat sink module proximate thesurface to be cooled 12. To permit visual inspection, at least a portionof the heat sink module 100 can be made of a transparent or translucentmaterial. In some examples, the transparent or translucent material canform the entire heat sink module 100, and in other examples, thetransparent or translucent material can form only a portion of the heatsink module, such as a window into the outlet chamber 150 of the heatsink module or a side wall of the heat sink module. In these examples,the window or side wall can permit boiling coolant within the outletchamber 150 to be observed when the heat sink module 100 is installed onthe surface to be cooled 12.

Orifices within Heat Sink Module

Each orifice 155 within the heat sink module 100 can include a centralaxis 74, as shown in FIG. 30. The central axis 74 of the orifice 155 mayeither be angled perpendicularly with respect to the surface to becooled 12 or angled non-perpendicularly with respect to the surface tobe cooled 12, the latter of which is shown in FIG. 30. FIG. 20 shows across-sectional view of a heat sink module with orifices 155 arranged ata 45-degree angle with respect to the surface to be cooled 12. If anglednon-perpendicularly with respect to the surface to be cooled 12, thecentral axis 74 of the orifice 155 may define any angle between 0° and90° with respect to the surface 12, such as about 5°, about 10°, about15°, about 20°, about 25°, about 30°, about 35°, about 40°, about 45°,about 50°, about 55°, about 60°, about 65°, about 70°, about 75°, about80° or about 85° or any range therebetween (e.g. 5-15°, 10-20°, 15-25°,20-30°, 25-35°, 30-40°, 35-45°, 40-50°, 45-55°, 50-60°, 55-65°, 60-70°,65-75°, 70-80°, or 75-85°). The orifice 155 may comprise anycross-sectional shape when viewed along its central axis 74. Variousexamples include a circular shape, an oval shape (to generate afan-shaped jet stream), a polygonal shape, or any other suitablecross-sectional shape.

FIG. 31 shows a top cross-sectional view of the heat sink module of FIG.21 taken along section C-C shown in FIG. 25. Section C-C passes throughthe dividing member 195 and exposes the array 76 of orifices 155 withinthe heat sink module 100. In this example, because the central axes 74of the plurality of orifices are arranged at a 45-degree angle withrespect to the dividing member 195, the orifices appear as ovals in FIG.31 despite the orifice being cylindrical coolant passageways through thedividing member.

The heat sink module 100 preferably includes an array 76 of orifices155. The central axes 74 of the orifices 155 in the array 76 may definedifferent angles with respect to the surface to be cooled 12.Alternately, the central axis 74 of each orifice 155 in the array 76 mayhave the same angle with respect to surface 12, as shown in FIG. 30. Insome examples, providing neighboring orifices with central axes 74 withthe same angle with respect to the surface to be cooled 12 can bepreferable to avoid interaction (i.e. interference) of the jet streams16 prior to impingement on the surface to be cooled 12. By providing jetstreams 16 that do not interfere with each other prior to impingement,the heat sink module 100 can provide jet streams 16 with sufficientmomentum to disrupt vapor formation on the surface to be cooled 12,thereby increasing the three-phase contact line length on the surface tobe cooled 12 and allowing higher heat fluxes to be effectivelydissipated without reaching critical heat flux.

The array 76 of orifices 155 may be arranged in any configurationsuitable for cooling the surface to be cooled 12. FIG. 62 shows possibleorifice 155 configurations including (a) a regular rectangular jet array76, (b) a regular hexagonal jet array 76, and (c) a circular jet array76. In the regular hexagonal array 76, shown in FIGS. 23, 31 and 62(b),the arrays 76 can be organized into staggered columns 77 and rows 78.The staggering of orifices 155 in the array 76 is such that a givenorifice 155 in a given column 77 and row 78 does not have acorresponding orifice in a neighboring row 78 in the given column 77 ora corresponding orifice 155 in a neighboring column 77 in the given row78. If the orifices 155 are configured to induce a substantially samedirection of flow 90 along the surface to be cooled 12 (as shown inFIGS. 30 and 32), the columns 77 and the rows 78 are preferably orientedsubstantially parallel and perpendicular, respectively, to thesubstantially same direction of flow 90. Arrays of orifices 155 innon-staggered arrangements can be used in other examples of the heatsink module 100.

The orifice 155 can be configured to project a jet stream 16 having anyof a variety of shapes and any of a variety of trajectories. With regardto shape, the stream 16 is preferably a symmetrical stream. As usedherein, “symmetrical stream,” refers to a jet stream 16 that issymmetrical in cross section. Examples of symmetrical streams includelinear streams, fan-shaped streams, and conical streams. Linear streamshave a substantially constant cross section along their length. Conicalstreams have a round cross section that increases along their length.Fan-shaped streams have a cross section along their length with a firstcross-sectional axis being significantly longer than a second,perpendicular cross-sectional axis. In some versions of the conical jetstreams 16, at least one and possibly both of the cross-sectional axesincrease in length along the length of the stream. With regard totrajectory, the jet stream 16 preferably comprises a central axis 17.For the purposes herein, the “central axis 17 of the stream 16” is theline formed by center points of a series of transverse planes takenalong the length of the stream 16, where each transverse plane isoriented to overlap with the smallest possible surface area of thestream 16, and each center point is the point on the transverse planethat is equidistant from opposing edges of the stream 16 along thetransverse plane. In preferred versions, the orifice 155 projects a jetstream 16 having a central axis 17 that is substantially collinear withthe central axis 74 of the orifice 155. However, the orifice 155 mayalso project a stream 16 having a central axis 17 that is angled withrespect to the central axis 74 of the orifice 155. The angle of thecentral axis 17 of the stream 16 with respect to the central axis 74 ofthe orifice 155 may be any angle between 0° and 90°, such as about 1°,about 2°, about 3°, about 4°, about 5°, about 7°, about 10°, about 15°,about 20°, about 25°, about 30°, about 35°, about 40°, about 45°, about50°, about 55°, about 60°, about 65°, about 70°, about 75°, or about 80°or any range therebetween. In such versions, the orifice 155 preferablyprojects a jet stream 16 where at least one portion of the jet stream 16is projected along the central axis 74 of the orifice 155. However, theorifice 155 may also project a jet stream 16 where no portions of thejet stream 16 are projected along the central axis 74 of the orifices155.

Similarly, the orifice 155 may be configured to project a jet stream 16that impinges on the surface 12 at any of a variety of angles. In someversions, the orifice 155 projects a stream 16 at the surface 12 suchthat the entire stream (in the case of a linear stream), or at least thecentral axis 17 of the stream 16 (in the case of conical or fan-shapedstreams), impinges perpendicularly on the surface 12 (i.e., at a 90°angle with respect to the surface). Perpendicular impingement upon asurface 12 induces radial flow of coolant 50 from contact points alongthe surface 12. While arrays 96 of perpendicularly impinging streams 16are suitable for some applications, they are not optimal in efficiency.This is because opposing coolant flow from neighboring contact pointsinteracts to form stagnant regions. Heat transfer performance in thesestagnant regions can fall to nearly zero, which in high heat fluxapplications (e.g. cooling high performance microprocessors or powerelectronics) can pose risks associated with critical heat flux.

In a preferred examples shown in FIGS. 30 and 32, the orifices 155 areconfigured to project jet streams 16 of coolant that impinge the surfaceto be cooled 12 such that at least the central axis 17 of each jetstream 16, and more preferably the entire jet stream 16, impingesnon-perpendicularly on the surface to be cooled 12 (i.e. at an angleother than 90° with respect to the surface), as shown in FIGS. 30-32. Asa non-limiting example, the central axis 17 of the jet stream 16 mayimpinge on the surface 12 at any angle between 0° and 90°, such as about1°, about 2°, about 3°, about 4°, about 5°, about 7°, about 10°, about15°, about 20°, about 25°, about 30°, about 35°, about 40°, about 45°,about 50°, about 55°, about 60°, about 65°, about 70°, about 75°, orabout 80° or any range there between.

FIG. 32 depicts a top view of a surface 12 on which jet streams 16 of anarray 76 of jet streams impinges non-perpendicularly on the surface 12.The non-perpendicular impingement creates a flow pattern 90 to the rightin which all the coolant 50 flows along the surface 12 in substantiallythe same direction 90. In some versions of patterns flowing insubstantially the same direction 90, flow of coolant 50 at each portionof the surface 12 has a common directional vector component along aplane defined by the surface to be cooled 12. In other versions, coolant50 at no two points on the surface 12 flows in opposite directions. Inyet other versions, coolant 50 at no two points on the surface 12 flowsin opposite directions or flows in perpendicular directions. Flowingcoolant 50 in the substantially same direction eliminates stagnantregions on the surface being cooled 12, which helps avoid the onset ofcritical heat flux.

The plurality of orifices 155 in the array 76 are preferably configuredto provide impinging jet streams 16 of coolant on the surface 12 in anarray 96 of contact points 91 (i.e. where each contact point 91 is a jetstream 16 impingement location on the surface to be cooled 12)comprising staggered columns 97 and rows 98, as shown in FIG. 32. Thestaggering is such that a given contact point 91 in a given column 97and row 98 does not have a corresponding contact point 91 in aneighboring column 97 in the given row 98 or a corresponding contactpoint 91 in a neighboring row 98 in the given column 97. If the coolant50 is induced to flow across the surface 12 in substantially the samedirection 90, as shown in FIG. 32, either the columns 97 or the rows 98are preferably oriented substantially perpendicularly to thesubstantially same direction 90 of flow. Arrays 96 of contact points 91arranged in this manner permit coolant 50 emanating from each contactpoint 91 in a given column 97 or row 98 to flow substantially betweencontact points 91 in a neighboring column 97 or row 98, respectively, asshown in FIG. 32. The heat sink module 100 shown in FIGS. 21 and 30provides even, consistent flow of coolant 50 over the surface to becooled 12, without formation of stagnation regions, and therebyencourages bubble 275 generation and evaporation, which dramaticallyincreases the heat transfer rate from the surface to be cooled 12.

The heat sink module 100 can include an array 76 of orifices 155 witheach orifice 155 having a central axis 74 angled non-perpendicularlywith respect to the surface 12, where each orifice 155 projects a jetstream 16 of coolant 50 having a central axis 17 collinear with thecentral axis 74 of the orifice 155. In some examples, all the orifices155 can have central axes 74 oriented at about the same angle and canproject jet streams 16 of coolant having about the same trajectory andshape and can impinge against the surface 12 at about the same angle ofimpingement.

The array 76 of orifices 155 can be provided within the heat sink module100 as illustrated and described with respect to FIGS. 23-31. Theplurality of jet streams 16 emitted from the plurality of orifices 155can promote bubble generation and evaporation at the surface to becooled 12, thereby achieving higher heat transfer performance thanconventional single-phase liquid cooling systems. Other implementationsmay promote bubble 275 generation using structures within the orifices155, such as structures that encourage cavitation or degassing ofnon-condensable gasses absorbed in the liquid. Similarlyboiling-inducing members 196 can be included in the heat sink module100, as shown in FIGS. 45-50, or can be included on the surface to becooled 12, as shown in FIG. 55.

Jet Streams with Entrained Bubbles

In some examples, it can be desirable provide jet streams 16 thatcontain entrained bubbles 275 to seed nucleation sites on the surface tobe cooled 12. Seeding nucleation sites on the surface to be cooled 12can promote vapor formation and can increase a heat transfer rate fromthe surface to be cooled 12 to the coolant 50. FIG. 73 shows a firstheat sink module 100 fluidly connected to a second heat sink module 100.A section of flexible tubing 225 transports coolant from an outlet port110 of the first heat sink module 100 to an inlet port 105 of the secondheat sink module 100. Within the first heat sink module 100, a pluralityof jet streams 16 of coolant are shown impinging a first surface to becooled 12. Due to heat transferring from the first surface to be cooled12 to the coolant 50 within in the outlet chamber 150 of the first heatsink module 100, vapor bubbles 275 form in the coolant 50. The bubbles275 can be dispersed within the liquid coolant as it exits the outletport 110 of the heat sink module 100. As the coolant 50 flows within thetubing 225 toward the inlet port 105 of the second heat sink module,some of the bubbles 275 may coalesce and form larger bubbles. The smalland large bubbles 275 can be transported to an inlet chamber 145 of thesecond heat sink module. The small bubbles may be sufficiently small totravel through the orifices 155 and become entrained in a jet streamthat impinges against the surface to be cooled. When the small bubblesimpinge the surface to be cooled 12, they may seed nucleation sites onthe surface to be cooled 12 and promote vapor formation, which canprovide higher heat transfer rates. In some examples, as shown in FIG.73, the larger bubbles 276 may be too large to pass through the orifices155. But pressure and flow forces may draw the larger bubbles 276 towardthe orifices 155, where upon contacting the orifice inlets, the largerbubbles 276 break into smaller bubbles that can pass through theorifices 155 and be entrained in the jet streams 16. In this way, thesize of the orifice 155 determines the maximum bubble size that will beentrained in the jet stream 16 and will impinge the surface to be cooled12. To provide jet streams 16 with entrained bubbles 275 that providedesirable seeding of nucleation sites on the surface to be cooled 12,the orifice 155 diameters within the heat sink module 100 can be about0.001-0.020, 0.001-0.2, 0.001-0.150, 0.001-0.120, 0.001-0.005, or0.030-0.050 in.

Anti-Pooling Orifices

Pooling of coolant 50 within the outlet chamber 150 of the heat sinkmodule 100 is undesirable, since it can create stagnation regions orother undesirable flow patterns that result in non-uniform cooling ofthe surface to be cooled 12, which can lead to critical heat fluxissues. To avoid pooling of coolant 50 in the outlet chamber 150, theheat sink module 100 can include a second plurality of orifices 156extending from the inlet chamber 145 to a rear wall (or proximate therear wall) of the outlet chamber 150, as shown in FIGS. 33-38. Thesecond plurality of orifices 156 can be configured to deliver aplurality of anti-pooling jet streams 16 of coolant to a rear portion ofthe outlet chamber 150 when pressurized coolant 54 is provided to theinlet chamber 145. As shown in FIG. 33, the second plurality of orifices156 can be arranged in a column along the rear wall of the outletchamber 150 thereby preventing coolant from pooling near the rear wallof the outlet chamber 150.

FIG. 35 shows a detailed view of one anti-pooling orifice 156 taken fromthe cross-sectional view of FIG. 34. The anti-pooling orifice 156 can beconfigured to deliver an anti-pooling jet stream 16 of coolant to a rearregion of the outlet chamber 150 to prevent coolant from pooling orstagnating near the rear wall of the outlet chamber 150. The centralaxes 75 of the anti-pooling orifice 156 can be arranged at an angle ofabout 0-90, 40-80, 50-70, or 60 degrees respect to the surface to becooled 12. In some examples, the central axes 75 of the anti-poolingorifice 156 can be at a larger angle than the central axes 74 of theplurality of orifices 155, as shown in FIG. 35. This arrangement canprevent interaction of the anti-pooling jet stream with a neighboringjet stream 16 prior to impingement on the surface to be cooled 12,thereby decreasing the likelihood of stagnation points on the surface tobe cooled 12 near the rear wall of the outlet chamber 150.

Boiling-Inducing Features

As described above, achieving boiling of coolant 50 proximate thesurface to be cooled 12 can dramatically increase the heat transfer rateand overall performance of the cooling apparatus 1. To encourage boilingof coolant 50 within the outlet chamber 150, the heat sink module 100can include one or more boiling-inducing members 196 extending from thebottom surface of the dividing member 195 toward the surface to becooled 12, as shown in FIG. 46. The one or more boiling-inducing members196 can be slender members extending from the bottom surface of thedividing member 195. In some examples, the one or more boiling-inducingmembers 196 can be configured to contact the surface to be cooled 12. Inother examples, the one or more boiling-inducing members 196 can beconfigured to extend toward the surface to be cooled but not contact thesurface to be cooled. Rather, a clearance can be provided between theone or more boiling-inducing members 196 and the surface to be cooled196, such that coolant 50 can flow between the surface to be cooled 12and the tips of the boiling-inducing members, thereby ensuring that nohot spots or stagnation regions are created on the surface to be cooled12. The clearance distance can be any suitable distance, and in someexamples can be 0.001-0.0125, 0.001-0.05, 0.001-0.02, 0.001-0.01, or0.005-0.010 in.

Angled Inlet and Outlet Ports

The inlet port 105 and outlet port 110 of the heat sink module 100 canbe angled to provide ease of installation in a wide variety ofapplications. For instance, when installing the heat sink module 100 ona microprocessor 415 that is mounted on a motherboard 405, as shown inFIG. 27, if the inlet port 105 of the heat sink module is arranged at anangle (a) that is greater than zero, a clearance distance is providedbetween a bottom surface of the inlet port 105 and the microprocessor415 and motherboard 405. This clearance distance can allow a connector120, such as a compression fitting, to be easily installed (e.g.threaded) on the inlet port 105) without interfering with or contactingthe microprocessor or motherboard. In addition, angling the port upwardsat a moderate angle reduces the likelihood that the heat sink module 100(and flexible tubing 225 connected to the inlet port 105) will interferewith any motherboard devices (e.g. capacitors, resistors, inductors),while still maintaining a compact height that allows the heat sinkmodule 100 to be used between two expansion cards. In the example shownin FIG. 21, a height measured from the bottom surface 135 to the topsurface 160 of the heat sink module 100 can be about 0.36 inches, and aheight measured from the bottom surface 135 to the highest surface ofthe angled inlet and outlet ports (105, 110) can be about 0.42 inches.As shown in FIGS. 5, 6, 56, and 57, free space can be limited on amotherboard 405 and in a server 400, and experimental installations haveshown that angled inlet and outlet ports (105, 110) and compact externaldimensions can be very helpful in making heat sink modules 100 fit intight spaces where competing heat sinks are unable to fit.

The heat sink module 100 can include an inlet port 105 that is fluidlyconnected to the inlet chamber 145 by an inlet passage 165. The heatsink module 100 can include a bottom plane 19 associated with the bottomsurface 135, as shown in FIG. 26. The inlet port 105 can be defined by acentral axis 23. The central axis 23 of the inlet port 105 can benon-parallel and non-perpendicular to the bottom plane 19 of the heatsink module 100. For instance, the central axis 23 of the inlet port 105can define an angle of about 10-80, 20-70, 30-60, or 40-50 degrees withrespect to the bottom plane 19 of the heat sink module 100.

The heat sink module 100 can include an outlet port 110 that is fluidlyconnected to the outlet chamber 150 by an outlet passage 166. The outletport 110 can be defined by a central axis 24, as shown in FIG. 29. Thecentral axis 24 of the outlet port 110 can be non-parallel andnon-perpendicular to the bottom plane 19 of the heat sink module 100.For instance, the central axis 24 of the outlet port 110 can define anangle of about 10-80, 20-70, 30-60, or 40-50 degrees with respect to thebottom plane 19 of the heat sink module 100.

Insertable Orifice Plate

In some instances, the heat sink module 100 can include two or morecomponents that are assembled to construct the heat sink module. Sincethe plurality of orifices 155 disposed in the dividing member 195 can bethe most intricate and costly portion of the heat sink module 100 tomanufacture (due to the relatively small diameters of the orifices 155requiring a tighter tolerance manufacturing process than the rest of themodule), it may be desirable to manufacture an orifice plate 198 (e.g.that includes a dividing member 195 and a plurality of orifices 155)separately from the rest of the heat sink module (i.e. the module body104) and subsequently assemble the module body 104 and the orifice plate198. FIG. 65 shows an insertable orifice plate 198 attached to a modulebody 104 to form heat sink module 100.

In some examples, the orifice plate 198 can be manufactured by a firstmanufacturing method and the module body 104 can be manufactured by asecond manufacturing method where the second manufacturing method is,for example, a lower cost and/or lower precision manufacturing methodthan the first manufacturing method. In some examples, the orifice plate198 can be manufactured by a 3-D printing process, and the module body104 can be manufactured by an injection molding process. In otherexamples, the orifice plate 198 can be manufactured by an injectionmolding process, a casting process, or a machining or drilling process,and the module body 104 can be manufactured by any other suitableprocess.

FIG. 65 shows a heat sink module 100 with a module body 104 and aninsertable orifice plate 198 installed therein. The insertable orificeplate 198 can be attached to the heat sink module 100 by any suitablemethod of assembly (e.g. fasteners, press fit, or snap fit). As shown inFIG. 65, the insertable orifice plate 198 can be pressed into the body104 of the heat sink module 100 and can include a sealing member 126that is configured to form a liquid-tight seal between the inlet chamber145 and the outlet chamber 150. In some examples, the insertable orificeplate 198 can be removable, and in other examples the insertable orificeplate 198 may not be easily removable once installed in the body of theheat sink module 100. The plurality of orifice 155 in the orifice plate198 can be optimized to cool a certain device, such as a certain brandand model of microprocessor 415 having a particular non-uniform heatdistribution. When the microprocessor 415, motherboard 405, or entireserver 400 is upgraded to a newer model, a first insertable orificeplate 198 in the heat sink module 100 can be replaced by a secondinsertable orifice plate 198 that has been optimized to cool the newermodel processor that will replace the older one. Consequently, insteadof needing to replace the entire heat sink module 100, only theinsertable orifice plate 198 needs to be replaced to ensure adequatecooling of the newer model processor. This approach can significantlyreduce costs associated with upgrading servers 400 in data centers 425.It can also significantly reduce the cost of optimizing the coolingapparatus 1 when replacing servers 400 in a datacenter 425, since theoriginal cooling apparatus 1, including the pump 20, manifolds (210,215), heat exchangers 40, flexible tubing 225, and fittings 235, cancontinue to be used.

A heat sink module 100 can be configured to cool a heat source, such asa surface 12 of a heat source. The heat sink module 100 can include aninlet chamber 145 formed within the heat sink module. The heat sinkmodule 100 can include an insertable orifice plate 198 and a module body104, as shown in FIG. 65, where the insertable orifice plate isconfigured to attach within the module body 104. The insertable orificeplate 198 can separate the inlet chamber 145 from an outlet chamber 150.The insertable orifice plate 198 can include a first plurality oforifices 155 passing from a top side of the insertable orifice plate 198to a bottom side of the insertable orifice plate 198. The firstplurality of orifices 155 can be configured to deliver a plurality ofjet streams 16 of coolant 50 into the outlet chamber 150 whenpressurized coolant 54 is provided to the inlet chamber 145 of the heatsink module 100. The outlet chamber 150 can have an open portionproximate a bottom surface of the heat sink module 100, and the openportion can be configured to be enclosed by a surface 12 of a heatsource when the heat sink module is installed on the surface of the heatsource. In this example, the first plurality of orifices 155 can have anaverage diameter of about 0.001-0.020, 0.001-0.2, 0.001-0.150,0.001-0.120, 0.001-0.005, or 0.030-0.050 in. The insertable orificeplate 198 can have a thickness of about 0.005-0.25, 0.020-0.1,0.025-0.08, 0.025-0.075, 0.040-0.070, 0.1-0.25, or 0.040-0.070 in.

Jet Height

The heat sink module 100 can have a bottom plane 19 associated with thebottom surface 135 of the heat sink module, as shown in FIG. 26. Thedistance between the bottom plane 19 of the heat sink module and thebottom side of the insertable orifice plate 198 (i.e. where orifice 155outlets are located) defines a “jet height” 18, which can be animportant factor affecting heat transfer rates attainable from thesurface to be cooled 12 in response to impinging jets 16 of coolant 50being delivered from the plurality of orifices 155. In some examples,the distance between the orifice 155 outlets and the surface to becooled 12 can be about 0.01-0.75, 0.05-0.5, 0.05-0.25, 0.020-0.25,0.03-0.125, 0.04-0.08, or about 0.050 in. In some examples, the jetheight 18 can define the height of the outlet chamber 150 of the heatsink module 100.

As shown in FIG. 26, the outlet chamber 150 can have a tapered profilethat permits for expansion of the coolant 50 as the coolant flowstowards the outlet port 110 and as the quality (x) of the coolantincreases in response to vapor formation proximate the surface to becooled 12. To provide this tapered volume, the bottom surface of thedividing member may be arranged at an angle with respect to the surfaceto be cooled. Consequently, a jet height 18 of a first orifice 155located near a front side of the heat sink module 100 may be less than ajet height 18 of a second orifice 155 located near a rear side of theheat sink module. In these examples, a non-uniform jet height 18 may bedefined as falling within a suitable range, such as about 0.01-0.75,0.05-0.5, 0.05-0.25, 0.020-0.25, 0.03-0.125, or 0.04-0.08 in. In otherexamples, an average jet height can be calculated based on thenon-uniform jet height values, and the average jet height can be about0.01-0.75, 0.05-0.5, 0.05-0.25, 0.020-0.25, 0.03-0.125, or 0.04-0.08 in.

In some examples, the distance between the bottom surface of theinsertable orifice plate 198 (or dividing member 195) and the bottomsurface 135 of the heat sink module 100 can define the jet height 18.The jet height (H) can be selected based on the average diameter (d_(n))of the plurality of orifices 155. The relationship between the jetheight 18 and the average diameter of the plurality of orifices 155 canbe expressed as a ratio (H/d_(n)). Examples of suitable values forH/d_(n) can be about 0.25-30, 0.25-10, 5-20, 15-25, or 20-30 for theheat sink module 100 described herein.

Jet Spacing

The orifices 155 within the heat sink module 100 can have any suitableconfiguration forming an array 76. FIGS. 62( a), (b), and (c) showconfigurations of orifices 155 having a rectangular jet array, ahexagonal jet array, and a circular jet array, respectively. Spacing (S)of the orifices 155 can be selected based on the average diameter(d_(n)) of the plurality of orifices 155. As shown in FIG. 62( b), for ahexagonal jet array 76, spacing between jets from left to right (i.e. ina streamwise direction for oblique jet impingement as shown in FIG. 32)is identified as S_(col), and spacing between jets from top to bottom(i.e. cross-stream direction for oblique impingement as shown in FIG.32) is identified as S_(row). Where S_(col) is set equal to S, andS_(row) is set equal to (2_(col)/√3), a relationship between jet spacingS and the average diameter of the plurality of orifices 155 can beexpressed as S/d_(n). Suitable values for S/d_(n) can be about 1.8-330,1.8-50, 25-125, 100-200, 150-250, 200-300, or 275-330 for therectangular, hexagonal, and circular jet arrays 76 shown in FIGS. 62(a), (b), and (c), respectively.

Internal Threads on Inlet and Outlet Ports

In some examples, corrugated, flexible tubing 225 can be used to fluidlyconnect heat sink modules 100 to the cooling apparatus. The corrugated,flexible tubing 225 can include spiral corrugations extending along thelength of the tubing 225, similar to course threads on a screw. Tofacilitate fast connection of a section of flexible tubing 225 to theheat sink module 100, corresponding corrugation-mating features can beprovided on the interior surfaces of the inlet and outlet ports (105,110) of the heat sink module. The corresponding corrugation-matingfeatures can be molded into the inlet and outlet ports (105, 110)thereby serving as internal threads. As a result, fluidly connecting asection of flexible corrugated tubing 225 to a port (105 or 110) of theheat sink module 100 can be as simple as threading the section of tubing225 into the port. In some examples the diameter of the port (105, 110)can taper inward, thereby ensuring a liquid-tight fit as the section oftubing 225 is threaded into the port. To further ensure a liquid-tightseal, a thread sealant, such as a Teflon tape or a spreadable threadsealant can be provided between the interior surface of the port (105,110) and the outer surface of the section of flexible tubing 225. Inother examples, an adhesive, such as epoxy, can be provided between theinterior surface of the port (105, 110) and the outer surface of thesection of flexible tubing 225 to further ensure a liquid-tight seal andto prevent inadvertent disconnection of the section of tubing from theport.

Leakproof Coating

The heat sink module 100 can be manufactured from a plastic materialthrough, for example, an injection molding process or an additivemanufacturing process. Depending of the properties of the plasticmaterial used to manufacture the heat sink module 100, and the type ofcoolant 50 used with the cooling apparatus 1 (and the molecular size ofthe coolant), leakage of coolant through the walls of the heat sinkmodule 100 may occur. To avoid leakage, the heat sink module 100 can becoated with a leakproof coating. In some examples, the leakproof coatingcan be a metalized coating, such as a nickel coating deposited on anouter surface of the heat sink module 100 or along the inner surfaces ofthe heat sink module (e.g. inner surfaces of the inlet and outlet ports,inlet and outlet passages, and inlet and outlet chambers). The leakproofcoating can be made of a suitable material and can have a suitablethickness to ensure that coolant does not migrate through the walls ofthe heat sink module 100 and into the environment. The leakproof coatingcan be applied to surfaces of the heat sink module 100 by any suitableapplication method, such as arc or flame spray coating, electroplating,physical vapor deposition, or chemical vapor deposition.

Internal Bypass in Heat Sink Module

To promote condensing of two-phase bubbly flow upstream of the reservoir200, and thereby reduce the likelihood of vapor being drawn into thepump 20 from the reservoir, the heat sink module 100 can include aninternal bypass that routes a portion of the coolant 50 flow deliveredto the inlet port 105 of the module around the heated surface 12. Theinternal bypass can be formed within the heat sink module 100. Forinstance, the internal bypass can be a, injection molded, cast, or 3Dprinted internal bypass formed within the heat sink module 100 andconfigured to transport coolant from the inlet port 105 to the outletport 110 without bringing the fluid in contact with the surface to becooled 12. The coolant that flows through the internal bypass can remainsingle-phase liquid coolant that is below the saturation temperature ofthe coolant. Near the outlet port 110 of the heat sink module 100, thesingle-phase liquid coolant that is diverted through the internal bypasscan be mixed with two-phase bubbly flow (i.e. two-phase bubbly flowgenerated by jet stream impingement against the surface to be cooled 12)that was not diverted. Mixing of the single-phase liquid coolant withthe two-phase bubbly flow can result in condensation and collapse ofvapor bubbles 275 within the mixed flow 50, thereby reducing the voidfraction of the coolant 50 flow delivered to the reservoir 200 and, inturn, reducing the likelihood of vapor bubbles being delivered to thepump 20.

In some examples, as shown in FIG. 12E, the internal bypass 65 in theheat sink module can include a pressure regulator 60. The pressureregulator 60 can be disposed at least partially within the internalbypass 65 and can serve to restrict flow through the internal bypass 65,thereby controlling the proportion of coolant flow through the internalbypass, and as a result, the proportion of coolant flow through theplurality of orifices 155 along a standard flow path 66 through the heatsink module. The internal pressure regulator 60 can be an active orpassive regulator. In some examples, the pressure regulator can be athermostatic valve that increases flow through the internal bypass 65 asthe temperature of the coolant increases or decreases. In otherexamples, the pressure regulator 60 can be computer controlled pressureregulator where flow is adjusted based on a temperature and/or apressure of the coolant upstream or downstream of the heat sink module100. In other examples, the pressure regulator 60 can be a simple flowconstriction (e.g. a physical neck) in the internal bypass thateffectively restricts flow by providing flow resistance.

Cooling Assembly

FIG. 7 shows a cooling assembly including a heat sink module 100 fluidlyconnected to two sections of flexible tubing 225. The heat sink module100 has an inlet port 105 and an outlet port 110. One end of the firstsection of flexible tubing 225 is fluidly connected to the inlet port105 by a first connector 120, and one end of the second section offlexible tubing 225 is fluidly connected to the outlet port 110 by asecond connector 120. In some examples, the connectors 120 can beliquid-tight fittings, such as compression fittings. The coolingassembly can be used to cool any heat generating surface associated witha device, such as an electrical or mechanical device.

Series-Connected Heat Sink Modules

FIG. 14A shows a schematic of a cooling apparatus 1 having three heatsink modules 100 arranged in a series configuration on three surfaces tobe cooled 12. As shown by way of example in FIG. 15, the three heat sinkmodules 100 can be fluidly connected with tubing, such as flexibletubing 225. The three surfaces to be cooled 12 can be three separatesurfaces to be cooled or can be three different locations on the samesurface to be cooled 12.

FIG. 15 shows a portion of a primary cooling loop 300 of a coolingapparatus 1 where the cooling loop 300 includes three series-connectedheat sink modules 100 mounted on three heat-providing surfaces 12 (see,e.g. FIG. 14A). The heat sink module 100 can be connected by sections offlexible tubing 225. A single-phase liquid coolant 50 can be provided toa first heat sink module 100 by a section of tubing 225-0, and due toheat transfer occurring within the first heat sink module 100-1 (i.e.heat being transferred from the first heat-generating surface 12 to theflow of coolant), two-phase bubbly flow can be generated and transportedin a first section of flexible tubing 225-1 extending from the firstheat sink module 100-1 to the second heat sink module 100-2. Thetwo-phase bubbly flow contains a plurality of bubbles 275 having a firstnumber density. Due to heat transfer occurring within the second heatsink module 100-2 (i.e. heat being transferred from the secondheat-generating surface 12 to the flow of coolant), higher quality (x)two-phase bubbly flow can be generated and transported from the secondmodule 100-2 to the third heat sink module 100-3 through a secondsection of flexible tubing 225-2. In the second section of flexibletubing 225, the two-phase bubbly flow contains a plurality of bubbles275 having a second number density, where the second number density ishigher than the first number density. Due to heat transfer occurringwithin the third heat sink module 100 (i.e. heat being transferred fromthe third heat-generating surface 12 to the flow of coolant), evenhigher quality (x) two-phase bubbly flow can be generated andtransported out of the third heat sink module 100-3 through a thirdsection of tubing 225-3. In the third section of tubing 225-3, thetwo-phase bubbly flow contains a plurality of bubbles 275 having a thirdnumber density, where the third number density is higher than the secondnumber density.

FIG. 14B shows a representation of coolant flowing through three heatsink modules (100-1, 100-2, 100-3) connected in series by four lengthsof tubing (225-1, 225-2, 225-3, 225-4), similar to the configurationsshown in FIGS. 14A and 15. FIG. 14B also shows corresponding plots ofsaturation temperature (T_(sat)), liquid coolant temperature(T_(liquid)), pressure (P), and quality (x) of the coolant versusdistance along a flow path through the series-connected heat sinkmodules. In the example, a flow 51 of single-phase liquid coolant 50enters the first heat sink module 100-1 through a first section oftubing 225-1 at a temperature that is slightly below the saturationtemperature of the liquid coolant 50. Within the first heat sink module100-1, the single-phase liquid coolant 50 is projected against a firstsurface to be cooled 12-1 by way of a plurality of jet streams 16 ofcoolant. A first portion of the liquid coolant 50 changes phase andbecomes vapor bubbles 275 dispersed in the liquid coolant 50, therebyproducing two-phase bubbly flow having a first quality (x₁). Thetwo-phase bubbly flow having the first quality is transported from thefirst heat sink module 100-1 to a second heat sink module 100-2 by asecond section of tubing 225-2. Within the second heat sink module100-2, the two-phase bubbly flow having a first quality is projectedagainst a second surface to be cooled 12-2 by way of a plurality of jetstreams 16 of coolant. A second portion of the liquid coolant 50 changesphase and becomes vapor bubbles 275 dispersed in the liquid coolant 50,thereby producing two-phase bubbly flow having a second quality (x₂)that is greater than the first quality (i.e. x₂>x₁). The two-phasebubbly flow having the second quality is transported from the secondheat sink module 100-2 to a third heat sink module 100-3 by a thirdsection of tubing 225-3. Within the third heat sink module 100-3, thetwo-phase bubbly flow having a second quality is projected against athird surface to be cooled 12-3 by way of a plurality of jet streams 16of coolant. A third portion of the liquid coolant 50 changes phase andbecomes vapor bubbles 275 dispersed in the liquid coolant 50, therebyproducing two-phase bubbly flow having a third quality (x₃) that isgreater than the second quality (i.e. x₃>x₂). As shown in FIG. 14B,along the distance of the flow path, quality of the coolant increases,pressure decreases, liquid coolant temperature (T_(liquid)) decreases,and T_(sat) decreases through successive series-connected heat sinkmodules.

Through each successive heat sink module 100, the flow of coolant 51experiences a pressure drop, as shown in FIG. 14B. In some examples, thepressure drop across each heat sink module 100 can be about 0.5-5.0,0.5-3, 1-3, or 1.5 psi. The pressure drop across each heat sink module100 causes a corresponding decrease in saturation temperature (Tsat) ofthe coolant. Accordingly, the temperature of the liquid coolantcomponent of the two-phase bubbly flow also decreases in response todecreasing saturation temperature at each pressure drop at each module.Consequently, the third heat sink module 100-3 receives two-phase bubblyflow containing liquid coolant 50 that is cooler than liquid coolant 50in the two-phase bubbly flow received by the second heat sink module100-2. As a result of this phenomenon, the cooling apparatus 1 is ableto maintain the third surface to be cooled 12-3 at a temperature belowthe temperature of a second surface to be cooled 12-2 when the secondand third surfaces to be cooled have equal heat fluxes. Because of thisbehavior, additional series connected heat sink modules 100 can be addedto the series configuration. In some examples four, six, or eight ormore heat sink modules 100 can be connected in series with eachsuccessive module receiving two-phase bubbly flow containing liquidcoolant 50 that is slightly cooler than the liquid coolant received bythe previous module connected in series. The only limitation on thenumber of series-connected modules that can be used a threshold quality(x) value, which if exceeded, could result in unstable flow. However, ifthe cooling system 1 is on the verge of exceeding the threshold quality(x) value, the coolant flow rate can be increased to decrease the flowquality.

HFE-7000 can be used as coolant 50 in the cooling apparatus 1. HFE-7000has a boiling temperature of about 34 degrees Celsius at a pressure of 1atm. In the example shown in FIGS. 14A, 14B, and 15, HFE-7000 can beintroduced to the series configuration as single-phase liquid coolant ata pressure of about 1 atmosphere and a temperature slightly below 34degrees Celsius. A flow rate of about 0.1-10, 0.2-5, 0.3-2.5, 0.6-1.2,or 0.8-1.1 liters per minute of single-phase coolant can be provided. Asthe coolant flows through the first, second, and third heat sinkmodules, the coolant may experience a total pressure drop of about 5-10,8-12, or 10-15 psi. At each heat sink module, the coolant may experiencea pressure drop of about 0.5-5.0, 0.5-3, 1-3, or 1.5 psi. As shown inFIG. 14B, a drop in saturation temperature accompanies each pressuredrop, and a drop in liquid temperature follows each decrease insaturation temperature. Consequently, the temperature of the liquidcomponent 50 of the two-phase bubbly flow continues to decrease throughthe series connection and exits the third heat sink module 100-3 at atemperature below 34 degrees Celsius, where the temperature depends onpressure and quality of the exiting flow 51. In this example, throughthe first heat sink module 100-1, heat transfer occurs via sensible andlatent heating of the coolant, and through the second and third heatsink modules (100-2, 100-3), heat transfer occurs primarily by latentheating of the coolant.

In competing pumped liquid cooling systems, such as those that usepumped single-phase water as a coolant, the coolant becomesprogressively warmer (due to sensible heating) as it passes through eachsuccessive series-connected heat sink module. For this reason, competingsingle-phase cooling systems typically cannot support more than twoseries connected heat sink modules, because the coolant temperature atthe outlet of the second heat sink module is too hot to properly cool athird heat sink module. Where competing pumped liquid cooling systemsinclude multiple series-connected heat sink modules, the cooling systemis unable to maintain sensitive devices, such as microprocessors, atuniform temperatures, and the last device in series may experiencesub-optimal performance or premature failure in response to operating atelevated temperatures.

FIG. 14C shows a representation of coolant flowing through three heatsink modules (100-1, 100-2, 100-3) connected in series by lengths oftubing (225-1, 225-2, 225-3, 225-4), similar to FIG. 14B, except thatthe coolant does not reach its saturation temperature until the secondheat sink module 100-2. Consequently, single-phase liquid coolant 50flows through the first heat sink module 100-1 (where no vapor isformed) and travels to the second heat-sink module 100-2 at an elevatedtemperature due to sensible heating. Within the second heat sink-module100-2, a pressure drop occurs, as does a corresponding drop insaturation temperature. Heat transfer from the second surface to becooled 12-2 to the single-phase liquid coolant 50 causes a portion ofthe coolant to vaporize. Consequently, heat transfer within the secondheat sink module 100-2 can be a combination of latent heating andsensible heating. Two-phase bubbly flow can then be transported from thesecond heat sink module 100-2 to the third heat sink module 100-3 in athird section of tubing 225-3. Within the third heat sink module 100-3,since the temperature of the liquid component 50 of the coolant is at ornearly at its saturation temperature, heat transfer may occur primarilyby latent heating, as evidenced by an increase in quality (x), as shownin FIG. 14C.

The method shown in FIG. 14C can be less efficient than the method shownin FIG. 14B, since it does not employ latent heating within the firstheat sink module 100-1 and may therefore require higher flow rates andmore pump work to adequately cool the first surface to be cooled 12-1.However, the method in FIG. 14C can be easier to achieve and maintain,since the temperature of the incoming single-phase liquid coolant 50does not need to be controlled as carefully as the method shown in FIG.14B (e.g. with respect to providing a temperature that is slightly belowthe saturation temperature). In some examples, an operating method canalternate between the methods shown in FIGS. 14B and 14C depending onthe temperature of the incoming single-phase coolant 50. For instance,where the system is undergoing transient operation, due to changing heatloads or changing chiller loop conditions, the operating method canalternate from the method shown in FIG. 14B to the method shown in FIG.14C for safety until the transient condition subsides. Once thetransient condition is over, the microcontroller 850 of the coolingapparatus 1 can begin to ramp up the temperature of the incomingsingle-phase liquid coolant 50 to a temperature that is slightly belowits saturation temperature. By employing this control strategy, thecooling system 1 can avoid instabilities caused by excess vaporformation during transient conditions. One strategy for decreasing thetemperature of the incoming single-phase liquid coolant 50 can includeincreasing the flow rate through the heat exchanger 40 to reduce thetemperature of the coolant in the reservoir 200, which is then deliveredto the series-configuration by the pump 20.

Parallel-Connected Heat Sink Modules

FIG. 16 shows a schematic of a cooling apparatus 1 having a primarycooling loop 300 that includes three parallel cooling lines where eachparallel cooling line includes three heat sink modules 100 fluidlyconnected in series. The cooling apparatus shown in FIG. 16 can beconfigured to cool nine independent heat-generating surfaces 12, such asnine microprocessors 415. Other variations of the cooling apparatus 1shown in FIG. 16 can include more than three parallel cooling lines, andeach cooling line can include more than three series-connected modules100.

As shown in the schematic of FIG. 16, additional heat sink modules 100can be added to the cooling apparatus 1 in parallel cooling loops 300that they are serviced by, for example, the same pump 20, reservoir 200,and heat exchanger 40. Alternatively, as shown in FIG. 17, the coolingapparatus 1 can include additional reservoirs 200, pumps 20, and/or heatexchangers 40 in parallel for the purpose of redundancy and reliability.As used herein, an additional component “in parallel” refers to acomponent in fluid communication with the other components in a mannerthat bypasses only components of the same type without bypassingdifferent types of components. An example of an additional componentadded in parallel is shown with the additional heat sink modules 100 inFIG. 16, where three parallel cooling loops 300 are provided that eachare serviced by the same reservoir 200 and pump 20.

Single Heat Sink Module for Multiple Heat Sources

To reduce installation costs, it can be desirable to cool more than oneheat source 12 using a single heat sink module 100. Exampleinstallations are shown in FIGS. 66 and 67. FIG. 66 shows an example ofan existing server 400 with a heat sink module retrofitted thereon. Theserver 400 includes a motherboard 405, two microprocessors 415 mountedon the motherboard, and a finned heat sink 440 mounted on eachmicroprocessor 415. Rather than spend time and effort removing thefinned heat sink modules 440 already installed on the microprocessors415, instead, a thermally conductive base member 430 can be placed inthermal contact with both finned heat sinks 440, as shown in FIG. 66.The thermally conductive base member 430 can extend from a first finnedheat sink 440 to a second finned heat sink 440. A heat sink module 100can be mounted on a surface 12 of the thermally conductive base member430. By directing a plurality of jet streams 16 of coolant at thesurface to be cooled 12 of the thermally conductive base member 430, theconfiguration shown in FIG. 66 can cool two microprocessorssimultaneously at a lower cost than installing two heat sink modules andwithout having to uninstall any factory-installed components of theserver (e.g. the finned heat sinks 440). By not uninstallingfactory-installed hardware, this cooling method can avoid potentiallyvoiding a factory warranty on the server 400 or computer.

FIG. 67 shows an arrangement where a thermally conductive base member430 extends from a first microprocessor 415 to a second microprocessor415 mounted on a motherboard 405. A heat sink module 100 can be mountedon a surface 12 of the thermally conductive base member 430. Bydirecting a plurality of jet streams 16 of coolant at the surface to becooled 12 of the thermally conductive base member 430, the configurationshown in FIG. 67 can cool two microprocessors 415 simultaneously at alower cost than using two heat sink modules. To ensure even cooling ofeach microprocessor, it can be desirable for the thermally conductivebase member 430 to make contact with an entire, or substantially theentire, top surface of each microprocessor, as shown in FIG. 67.

Surface to be Cooled

The surface to be cooled 12 can be exposed within the outlet chamber 150of the heat sink module 100, such that the jet streams 16 of coolant 50impinge directly on the surface to be cooled 12 without thermalinterference materials disposed between the surface 12 and the coolant50. As used herein, “surface to be cooled” refers to any electronic orother device having a surface that generates heat and requires cooling.Non-limiting, exemplary surfaces to be cooled 12 include microprocessors415, microelectronic circuit chips in supercomputers, power electronics,mechanical components, process containers, or any electronic circuits ordevices requiring cooling, such as diode laser packages. The surface tobe cooled 12 can be exposed within the outlet chamber 150 of the heatsink module 100 by constructing the outlet chamber to include thesurface 12 within the chamber 150 or by constructing the outlet chambersuch that the surface to be cooled 12 serves as a bounding wall of theoutlet chamber 150, as shown in FIG. 26. In some examples, the heat sinkmodule 100 can form an enclosure, such as a sealed liquid-tightenclosure, against the surface to be cooled 12 using one or more sealingmembers (e.g. o-rings, gaskets, or adhesives).

In some examples of the cooling apparatus 1, coolant 50 can be deliveredto a heat sink module 100 that is mounted directly on a surface to becooled, such as a surface of a microprocessor 415 that is electricallyconnected to a motherboard 405, as shown in FIG. 27. In other examples,the heat sink module 100 can be mounted on a thermally conductiveintermediary object, such as a thermally conductive base member 430, asshown in FIG. 26. The assembly of the heat sink module 100 and thethermally conductive base member 430 can then be mounted on a heatsource, such as a microprocessor 415 electrically connected to amotherboard 405, as show in FIG. 28. A layer of thermal interfacematerial (e.g. solder thermal interface material or polymer thermalinterface material) can be applied between a top surface of the heatsource (e.g. microprocessor) and a bottom surface of the thermallyconductive base member 430. The thermally conductive base member 430 canbe made of a material with a high thermal conductivity, such as copper,silver, gold, aluminum, or tungsten.

The thermally conductive member 430 can be placed in thermalcommunication with an electronic device, or other type of device, thathas a surface 12 that generates heat and requires cooling, such as amicroprocessor 415, microelectronic circuit chip in a supercomputer, orany other electronic circuit or device requiring cooling, such as diodelaser packages.

Three-Phase Contact Line Length

FIG. 63 shows a top view of a heated surface 12 covered by coolant 50,where the coolant has regions of vapor coolant 56 and wetted regions ofliquid coolant 57 in contact with the heated surface 12. The dark areasin FIG. 63 show the vapor coolant regions 56, and the light areas showthe liquid coolant regions 57. A length of a three-phase contact line 58is measured as a sum of all curves where liquid coolant 57, vaporcoolant 56, and the solid heated surface 12 are in mutual contact on theheated surface 12. The three-phase contact line 58 length can bedetermined using suitable image processing techniques.

The heat transfer rate from the surface to be cooled 12 to the coolant50 has been shown to strongly correlate with the length of thethree-phase contact line 58 on the surface to be cooled 12.Consequently, increasing the length of the three-phase contact line 58can be desirable when attempting to increase the heat transfer rate fromthe surface to be cooled. Increasing the heat transfer rate isdesirable, since it increases the efficiency of the cooling apparatus 1and allows higher heat flux surfaces to be cooled by the coolingapparatus.

By providing jet streams 16 of coolant that impinge the surface to becooled 12 from a suitable jet height 18, the heat sink modules 100described herein effectively increase the length of the three-phasecontact line 58. Consequently, the heat sink modules 100 describedherein provide much higher heat transfer rates than competing coolingsystems. By selecting orifice 155 diameters, jet heights 18, coolantpressures, and orifice orientations from the ranges provided herein, theheat sink module 100 can provide jet streams 16 with sufficient momentumto disrupt vapor formation on the surface to be cooled 12, therebyincreasing the length of the three-phase contact line 58 on the surfaceto be cooled 12 and thereby allowing higher heat fluxes to beeffectively dissipated without reaching critical heat flux.

Redundant Cooling Apparatus

In some examples, it can be desirable to have a fully redundant coolingapparatus 1 where each heat-generating surface 12 is cooled by at leasttwo completely independent cooling loops 300. In the event of failure ofa first independent cooling loop 300, a second independent loop can beconfigured to provide sufficient cooling capacity to adequately cool theheat-generating surface 12 and thereby avoid any downtime or reductionin performance when the heat-generating surface 12 is, for example, amicroprocessor 415 or other critical system component. In a fullyredundant cooling apparatus 1, the heat-generating component 12 beadequately cooled by a first cooling apparatus (and can continue tooperate normally) while repairs are made on a failed component within asecond cooling apparatus of the redundant cooling apparatus 1.

FIG. 9 shows a front perspective view of a fully redundant coolingapparatus 1 installed on eight racks 410 of servers 400 in a data center425. The redundant cooling apparatus 1 includes two independent primarycooling loops 300, each similar to the primary cooling loop describedwith respect to FIGS. 1-3. FIG. 10 shows a rear view of the redundantcooling apparatus 1 of FIG. 9. In FIGS. 9 and 10, the redundant coolingapparatus has an independent pump 20, an independent reservoir 200, andan independent heat exchanger 40 associated with each independentprimary cooling loop 300. However, in some examples, the primary coolingloops 300 may be fluidly connected and may share a common reservoir 200and/or a common heat exchanger 40. Such an arrangement may be neededwhere redundant cooling loops 300 are desired but where safetyregulations restrict the volume of coolant that can be used in aconfined space.

FIG. 18 shows a schematic of a redundant cooling apparatus 1 with afirst primary cooling loop 300 that includes two parallel cooling lineswhere each parallel cooling line is fluidly connected to three redundantheat sink modules 700 arranged in series, and a second primary coolingloop 300 that includes two parallel cooling lines where each parallelcooling line is fluidly connected to the three redundant heat sinkmodules 700 arranged in series.

FIG. 19 shows a top view of a redundant cooling apparatus installed in adata center or computer room 425 having twenty racks 410 of servers 400.Each primary cooling loop 300 of the redundant cooling apparatus 1 canbe fluidly connected to a heat exchanger 40 located inside of the room425 where the servers are located. In some examples, the heat exchangercan dump heat into the room 425, and a CRAC can be used to remove theheat from the room.

FIG. 20 shows a top view of a redundant cooling apparatus installed in adata center or computer room 425 having twenty racks 410 of servers 400.Each primary cooling loop 300 of the redundant cooling apparatus can befluidly connected to a heat exchanger 40 located outside of the room 425where the servers are located. In some examples the heat exchanger 40can be connected to a chilled water system of a building. In otherexamples, the heat exchanger 40 can be connected to an air conditioningunit located outside of the room 425 (e.g. outside of the building).

Redundant Heat Sink Module

FIG. 51A shows a top perspective view of a redundant heat sink module700. FIG. 51B shows a top view of the redundant heat sink module of FIG.51A, where a first independent flow path 701 and the second independentflow path 702 are represented by dashed lines. In the example shown inFIG. 51B, the first independent flow path 701 passes through a firstregion near a middle of the redundant heat sink module 700, and thesecond independent flow path 702 passes through a second region outsideof the perimeter of the first region. The first and second independentflow paths (701, 702) can be completely independent, meaning that noamount (or no substantial amount) of coolant 51 transfers from the firstindependent flow path to the second independent flow path or vice versa.The first independent flow path can extend from a first inlet port 105-1to a first outlet port 110-1. Similarly, a second independent flow path702 can extend from a second inlet port 105-2 to a second outlet port110-2.

The first independent flow path 701 can include a first inlet passage165-1 extending from the first inlet port 105-1 to a first inlet chamber145-1. A first plurality of orifices 155-1 can extend from the firstinlet chamber 145-1 to a first outlet chamber 150-1 and can beconfigured to provide a plurality of jet streams 16 of coolant into thefirst outlet chamber 150-1 when pressurized coolant is provided to thefirst inlet chamber 145-1. A first outlet passage 166-1 can extend fromthe first outlet chamber 150-1 to the first outlet port 110-1. A firstplurality of anti-pooling orifices 156-1 can extend from the first inletchamber 145-1 to a location proximate a rear wall of the first outletchamber 150-1 and can be configured to provide a plurality of jetstreams 16 of coolant proximate a rear wall of the first outlet chamber150-1 when pressurized coolant is provided to the first inlet chamber145-1.

The second independent flow path 702 can include a second inlet passage165-2 extending from the second inlet port 105-2 to a second inletchamber 145-2. A second plurality of orifices 155-2 can extend from thesecond inlet chamber 145-2 to a second outlet chamber 150-2 and can beconfigured to provide a plurality of jet streams 16 of coolant into thesecond outlet chamber 150-2 when pressurized coolant is provided to thesecond inlet chamber 145-2. A second outlet passage 166-2 can extendfrom the second outlet chamber 150-2 to the second outlet port 110-2. Asecond plurality of anti-pooling orifices 156-2 can extend from thesecond inlet chamber 145-2 to a location proximate a wall of the secondoutlet chamber 150-2 and can be configured to provide a plurality of jetstreams 16 of coolant proximate the wall of the second outlet chamber150-2 when pressurized coolant is provided to the second inlet chamber145-2.

FIG. 51D shows a bottom view of the redundant heat sink module 700 ofFIG. 51A. The first independent flow path 701 includes an array oforifices 155 arranged in a first region located near a middle portion ofthe module 700. The second independent flow path 702 includes an arrayof orifices 155 arranged in a second region located beyond (e.g. outsideof) the perimeter of the first region. In other examples, the firstregion can be located near a first half of the module 700 and the secondregion can be located near a second half of the module 700, as shown inthe parallel path example of FIG. 53.

The first outlet chamber 150-1 of the redundant heat sink module 700 canhave an open portion that can be enclosed by a surface to be cooled 12when the redundant heat sink module 700 is installed on a surface to becooled. Similarly, the second outlet chamber 150-2 of the redundant heatsink module 700 can have an open portion that can be enclosed by asurface to be cooled 12 when the redundant heat sink module 700 isinstalled on a surface to be cooled. To facilitate sealing against thesurface to be cooled 12, the heat sink module can include a firstsealing member 125-1 and a second sealing member 125-2, as shown in FIG.51D. The first sealing member 125-1 (e.g. o-ring, gasket, sealant) canbe disposed within a first channel 140-1 formed in a bottom surface 135of the redundant heat sink module 700. The first channel 140-1 cancircumscribe the first outlet chamber 150-1, and the first sealingmember 125-1 can be compressed between the first channel 140-1 and thesurface to be cooled 12 to provide a liquid-tight seal therebetween. Theredundant heat sink module 700 can include a second sealing member125-2, as shown in FIG. 51D. The second sealing member 125-2 (e.g.o-ring, gasket, sealant) can be disposed within a second channel 140-2formed in the bottom surface 135 of the redundant heat sink module 700.The second channel 140-2 can circumscribe the second outlet chamber150-2, and the second sealing member 125-2 can be compressed between thesecond channel 140-2 and the surface to be cooled 12 to provide aliquid-tight seal therebetween. In this example the first sealing member125-1 can provide a liquid-tight seal between the first outlet chamber150-1 and the second outlet chamber 150-2).

FIG. 51F shows a side cross-sectional view of the redundant heat sinkmodule 700 of FIG. 51A taken along section A-A shown in FIG. 51E. FIG.51G shows a side cross-section view of the redundant heat sink module700 of FIG. 51A taken along section B-B shown in FIG. 51E. FIG. 51Ishows a cross-sectional view of the redundant heat sink module 700 ofFIG. 51A taken along section C-C shown in FIG. 51H. FIG. 51K shows aside cross-sectional view of the redundant heat sink module of FIG. 51Ataken along section D-D shown in FIG. 51J. FIG. 51M shows a sidecross-section view of the redundant heat sink module 700 of FIG. 51Ataken along section E-E of FIG. 51L.

FIG. 17 shows a schematic of a redundant cooling apparatus 1 having aredundant heat sink module 700 mounted on a heat source 12. Theredundant heat sink module 700 is connected to two independent primarycooling loops 300. In another example, the redundant heat sink module700 can be replaced with two separate heat sink modules 100, where afirst heat sink module 100 is connected to a first independent primarycooling loop 300, and a second heat sink module 100 is connected to asecond independent primary cooling loop 300.

Portable Servicing Unit

A portable servicing unit can be provided to aid in draining the coolingapparatus 1, for example, when servicing or repairing the coolingapparatus. The portable servicing unit can include a vacuum pump. Theportable servicing unit can include a hose, such as a flexible hose,having a first end a second end. A first end of the hose can beconfigured to fluidly connect to an inlet of the vacuum pump of theportable servicing unit. A second end of the hose can be configured tofluidly connect to a connection point (e.g. a drain 245) of the coolingapparatus 1 through, for example, a threaded fitting or a quick-connectfitting. The portable machine can include a portable reservoir fluidlyconnected to an outlet of the vacuum pump. When connected to the coolingapparatus 1 and activated, the vacuum pump of the portable servicingunit can apply vacuum pressure to the cooling apparatus 1 by way of thehose, which results in coolant flowing from the cooling apparatus,through the hose and vacuum pump, and into the portable reservoir. Whenservicing is complete, fluid from the portable reservoir can be pumpedback into the cooling system or transported to an appropriate disposalor recycling facility. In some examples, the portable servicing unit caninclude one or more thermoelectric heaters. The thermoelectric heaterscan be placed in thermal communication with components of the coolingapparatus 1, and by transferring heat to coolant within the apparatus,the thermoelectric heaters can promote evacuation of fluid from theapparatus through a drain 245 or other access point in the apparatus.

3-D Printing

One or more components of the cooling apparatus 1 can be manufactured bya three-dimensional printing process, also known as additivemanufacturing. The heat sink module 100, or portions of the heat sinkmodule, such as an insertable orifice plate 198, can be manufactured bya three-dimensional printing process. In some examples, athree-dimensional manufacturing process can be used to create tubing 225used to fluidly connect a first heat sink module 100 to a second heatsink module, such as the section of tubing shown in FIG. 73. In someexamples, a three-dimensional printing process can be used to form acombined heat sink module 100 and section of tubing 225. In someexamples, a three-dimensional printing process can be used to form twoheat sink modules 100 fluidly connected by a section of tubing 225, asshown in FIG. 73. This approach can eliminate potential leak points thatwould typically exist, for example, at threaded connections wherefittings attach a section of tubing 225 to an inlet or outlet port (105,110) of the heat sink modules. This approach can also reduceinstallation time and reduce risk of installation error.

In some examples, components of the cooling apparatus 1 can be formed bya stereolithography process that involves forming layers of materialcurable in response to synergistic stimulation adjacent to previouslyformed layers of material and successively curing the layers of materialby exposing the layers of material to a pattern of synergisticstimulation corresponding to successive cross-sections of the heat sinkmodule. The material curable in response to synergistic stimulation canbe a liquid photopolymer.

Coolant Temperature, Pressure, and Flow Rate

In some examples, it can be desirable to maintain coolant surrounding asurface to be cooled 12 at a pressure that results in the saturationtemperature of the coolant being slightly above the temperature of jetstreams of coolant being projected at the surface to be cooled 12. Asused herein, “maintain” can mean holding at a relatively constant valueover a period of time. “Coolant surrounding a surface” refers to asteady state volume of coolant immediately surrounding and in contactwith the surface to be cooled 12, excluding jet streams 16 of coolantprojected directly at the surface to be cooled 12. “Saturationtemperature” is used herein as is it is commonly used in the art. Thesaturation temperature is the temperature for a given pressure at whicha liquid is in equilibrium with its vapor phase. If the pressure in asystem remains constant (i.e. isobaric), a liquid at saturationtemperature evaporates into its vapor phase as additional thermal energy(i.e. heat) is applied. Similarly, if the pressure in a system remainsconstant, a vapor at saturation temperature condenses into its liquidphase as thermal energy is removed. The saturation temperature can beincreased by increasing the pressure in the system. Conversely, thesaturation temperature can be lowered by decreasing the pressure in thesystem. In specific versions of the invention, a saturation temperature“slightly above” the temperature of jet streams 16 of coolant projectedat the surface to be cooled 12 refers to a saturation temperature ofabout 0.5° C., about 1° C., about 3° C., about 5° C., about 7° C., about10° C., about 15° C., about 20° C., or about 30° C. above thetemperature of coolant 50 projected against the surface. Establishing asaturation temperature of coolant 50 surrounding a surface 12 slightlyabove the temperature of the jet stream 16 of coolant projected at thesurface provides for at least a portion of the coolant projected at thesurface to heat and evaporate after contacting the surface, therebygreatly increasing the heat transfer rate and efficiency of the coolingapparatus 1.

The appropriate pressure at which to maintain the coolant to achieve thepreferred saturation temperatures can be determined theoretically byrearranging the following Clausius-Clapeyron equation to solve for P₀:

$T_{B} = \left( {\frac{R\; {\ln \left( P_{0} \right)}}{\Delta \; H_{vap}} + \frac{1}{T_{0}}} \right)^{- 1}$

where:

-   -   T_(B)=normal boiling point, K    -   R=ideal gas constant, 8.3145 J·K⁻¹ mol⁻¹    -   P₀=vapor pressure at a given temperature, atm    -   ΔH_(vap)=heat of vaporization of the coolant, J/mol    -   T₀=given temperature, K    -   Ln=that natural logarithm to the base e.

In the above equation, the given temperature (T₀) is the temperature ofcoolant 50 in contact with, and heated by, the surface to be cooled 12.The normal boiling point (T_(B)) is the boiling point of the coolant ata pressure of one (1) atmosphere. The heat of vaporization (ΔH_(vap)) isthe amount of energy required to convert or vaporize a given quantity ofa saturated liquid (i.e., a liquid at its boiling point) into a vapor.As an alternative to determining the appropriate pressure theoretically,the appropriate pressure can be determined empirically by adjusting thepressure and detecting evaporation or bubble generation at a surface tobe cooled 12, as shown in FIG. 30. Bubble generation can be visuallydetected with a human eye when transparent components, such as atransparent heat sink module 100 or transparent flexible tubing 225, isused to construct the cooling apparatus 1. In some examples, the heatsink module 100 or the flexible tubing 225 can be transparentthroughout, and in other examples, at least a portion of the heat sinkmodule 100 or flexible tubing 225 can be transparent to provide atransparent window portion that permits a system operator or electroniceye to visually detect the presence of bubbles 275 within the coolant 50flow and to make system adjustments based on that visual detection. Forinstance, if no bubbles 275 are visually detected exiting the outletchamber 150 of the heat sink module 100, the coolant flow rate can bereduced by reducing the pump 20 speed, thereby reducing energy consumedby the pump 20 and reducing overall energy consumption and operatingcost. Conversely, if slug or churn flow is detected (see, e.g. FIGS. 58and 59B), the coolant flow rate 51 can be increased to eliminate thepresence of those unwanted flow regimes and restore the system totwo-phase bubbly flow.

During operation of the cooling apparatus 1, coolant 50 can be flowedinto an outlet chamber 150 of the heat sink module 100. The surface tobe cooled 12 can be exposed within the outlet chamber 150 or, as shownin FIG. 30, the surface to be cooled 12 can serve as a bounding surfaceof the outlet chamber 150 when the heat sink module 100 is installed onthe surface to be cooled 12. The coolant 50 can be introduced to theoutlet chamber 150 at a predetermined pressure that promotes a phasechange upon the liquid coolant 50 contacting, and being heated by, thesurface to be cooled 12. One example of such a cooling apparatus 1 forperforming various cooling methods described herein is shown in FIG.11A. The cooling apparatus 1 can include a heat sink module 100, asshown in FIGS. 26 and 30. The heat sink module 100 can include an outletchamber 150 with a surface 12 to be cooled exposed within the outletchamber 150. The pump 20, as shown in FIG. 11A, can provide coolant 50at a predetermined pressure to an inlet 21 of the heat sink module 100.

The cooling apparatus 1 as described above and as shown in FIG. 11A caninclude several steady-state zones comprising either liquid flow ortwo-phase bubbly flow. The nature of the coolant 50 in each zone candepend on the temperature and pressure of the coolant in each zone. Inthe example in FIG. 11A, a zone comprising high-temperature coolant 52includes the coolant 50 surrounding the surface to be cooled 12 withinthe outlet chamber 150 (excluding the jet streams 16 of coolant 50projected into the outlet chamber 150 through the orifices 155 of theheat sink module 100) of the heat sink module 100 and extends downstreamto the heat exchanger 40 (see FIG. 11A for direction of flow 51).Portions of the high-temperature coolant 52 within the outlet chamber150 are preferably at a temperature approximately equal to or above thesaturation temperature. A zone of low-temperature coolant 53 extendsfrom downstream of the reservoir 200 to at least the inlet port 105 ofthe first heat sink module 100 and includes the jet streams 16 ofcoolant 50 injected into the outlet chamber 150 of the first heat sinkmodule 100. The low-temperature coolant 53 is preferably at atemperature slightly below the saturation temperature of the coolant 50surrounding the surface 12, wherein “slightly below” can include 0.5-1,0.5-3, 1-3, 1-5, 3-7, 5-10, 7-10, 7-15, 10-15, 15-20, 15-30, about 0.5,about 1, about 3, about 5, about 7, about 10, about 15, about 20, orabout 30° C. or more below the saturation temperature of coolant 50surrounding the surface to be cooled 12. Heat transfer from the surfaceto be cooled 12 to the coolant 50 with the outlet chamber 150 of theheat sink module 100 serves to transition the low-temperature coolant 53to high-temperature coolant 52. In some examples, the surface to becooled 12 heats a portion of the coolant 50 contacting the surface 12 toits saturation temperature, thereby promoting evaporation and formationof two-phase bubbly flow, which exits the heat sink module through theoutlet port 110.

A zone of low-pressure coolant 55 includes the coolant 50 surroundingthe surface to be cooled 12 within the outlet chamber 150 (whichexcludes the jet streams 16 of coolant 50 projecting into the outletchamber 150 through the orifices 155 of the heat sink module) andextends downstream to an inlet 21 of the pump 20. The low-pressurecoolant 55 is preferably at a pressure that promotes evaporation ofcoolant 50 when heated at the surface 12. Therefore, the pressure of thelow-pressure coolant 55 preferably determines a saturation temperatureto be about equal to the temperature of the high-temperature coolant 52.A zone of high-pressure coolant 54 includes a portion downstream of thepump outlet 22 and extends to at least the inlet port 105 of the firstheat sink module 100. The high-pressure coolant 54 is preferably at apressure suitable for generating jet streams 16 of coolant that arecapable of penetrating liquid present in the outlet chamber 150 andimpinging the surface to be cooled 12. In some examples, the pump 20 canprovide high-pressure coolant 54 at a pressure of about 1-20, 10-30,25-50, 40-60, or 50-75, 60-80, or 75-100 psi. In other examples, thepump 20 can provide high-pressure coolant 54 at a pressure of about85-120, 100-140, 130-160, 150-175, 160-185, 175-200, or greater than 200psi.

The pump 20 serves to transition low-pressure coolant 55 tohigh-pressure coolant 54 as the coolant passes from the pump inlet 21 tothe pump outlet 22. In some examples, the pump 20 can providehigh-pressure coolant 54 at a pressure that is about 10-20, 15-30,20-40, 30-45, or 40-60 psi or greater above the pressure of thelow-pressure coolant 55. The high-pressure coolant 54 in the coolingapparatus 1 applies a positive pressure against the plurality oforifices 155 in the heat sink module 100, and the plurality of orifices155 serve to transition the high-pressure coolant 54 to low-pressurecoolant 55, as the coolant 50 equilibrates to the pressure of thelow-pressure coolant 55 after passing through the plurality of orificesas jet streams 16 and mixing with the coolant in the outlet chamber 150of the heat sink module 100.

With the apparatus 1 described above, a flow rate is set by the pump 20to handle the expected heat load produced by the surface to be cooled12. A specific pressure for the low-pressure coolant 55 is set andmaintained by one or more pumps 20 and by one or more pressureregulators 60, as shown in the various schematics presented in FIGS.11A-14, 16-18, and 68-72 to establish a saturation temperature for thecoolant 50 surrounding the surface to be cooled 12 to be slightly abovethe saturation temperature of the low-temperature coolant 53. Relativelyhigh-pressure 54 low-temperature 53 coolant 50 is projected as jetstreams 16 from the plurality of orifices 155 against the surface to becooled 12, whereby the coolant 50 undergoes a pressure drop uponequilibrating with fluid present in the outlet chamber 150 and a portionof the fluid may heat to its saturation temperature upon contacting thesurface 12 and absorbing heat from the surface. A portion of the heatedcoolant 50 undergoes a phase transition at the surface to be cooled 12,which causes highly efficient cooling of the surface 12. Downstream ofthe heat sink module 100, the relatively low-pressure 55,high-temperature 52 coolant flow is then mixed with low-pressure 55,low-temperature 54 coolant from the second bypass 310 to promotecondensing of vapor bubbles 275 within the low-pressure 55, hightemperature 52 coolant by cooling it below its saturation temperature,which produces a flow of low-pressure 55, low-temperature 53 coolant inthe return line 230 that returns the coolant 50 to the reservoir 200.Upon being drawn form the lower portion of the reservoir 200 to the pumpinlet 21, the low-pressure 55, low-temperature 53 coolant is thentransitioned to high-pressure 54, low-temperature 53 coolant as itpasses through the pump 20. The high-pressure 54, low-temperature 53coolant is then circulated back to the inlet port 105 of the first heatsink module 100 and the above-described process is repeated.

Cooling System Preparation and Operation

In some applications, it can be desirable to fill the cooling apparatus1 with a dielectric coolant 50 that is at a pressure below atmosphericpressure (e.g. less than about 14.7 psi). For example, when coolingmicroprocessors 415, it can be desirable fill the cooling apparatus 1with HFE-7000 (or a coolant mixture containing HFE-7000 and, forexample, R-245fa) that is at a pressure below atmospheric pressure toreduce the boiling point of the dielectric fluid. To accomplish this,the portable servicing unit (or other vacuum source) can be used toapply a vacuum to the cooling apparatus 1 to purge the contents of thecooling apparatus. Upon reducing the pressure within the coolingapparatus 1 to about 0-3, 0-5, 1-5, 4-8, 5-10, or 8-14.5 psi, thedielectric coolant 50 can be added to the cooling apparatus 1. In someexamples, operation of the pump 20 may only increase the pressure of thedielectric coolant about 1-15, 5-20, or 10-25 psi above the baselinesub-atmospheric pressure. Consequently, the operating pressure of thehigh pressure coolant 54 within the cooling apparatus 1 may be aboutequal to atmospheric pressure (e.g. about 8-14, 10-16, 12-18, or 14-20psi), thereby ensuring that that saturation temperature of thedielectric coolant remains low enough to ensure that boiling can beachieved when jet streams 16 of coolant impinge the surface to be cooled12 associated with a microprocessor 415. Providing high-pressure coolant54 at a pressure near atmospheric pressure has other added benefits.First, low pressure tubing 225 can be used, which is lightweight,flexible, and low cost. Second, because of the minimal pressuredifference between the high-pressure coolant 54 and the surroundingatmosphere, fluid leakage from fittings and other joints of the coolingapparatus 1 may be less likely.

Heat Exchanger

The cooling apparatus 1 can include a heat exchanger 40 in fluidcommunication with the bypass 305. In some examples, the heat exchanger40 can be upstream of the pressure regulator 60 in the bypass 305, andin other examples, the heat exchanger 40 can be downstream of thepressure regulator 60 in the bypass 305. “Downstream” and “upstream” areused herein in relation to the direction of flow 51 of coolant 50 withinthe cooling apparatus 1. Any heat exchanger 40 capable of reducing thetemperature of the coolant 50 to below its saturation temperature isacceptable. Non-limiting examples include shell-and-tube, plate,adiabatic-wheel, plate-fin, pillow-plate, fluid,dynamic-scraped-surface, phase-change, direct contact, and spiral heatexchangers. The heat exchanger 40 can operate by parallel flow orcounter flow. An air-to-liquid heat exchanger 40 can be a fin-and-tubetype, a micro-channel type, or any other suitable air-to-liquid type ofheat exchanger.

In some examples, the heat exchanger 40 can be an air-to-liquid heatexchanger having a fan 26 mounted thereon to increase the rate of heattransfer between the working fluids (i.e. between the coolant 50 and theambient air), as shown in FIGS. 12P, 12Q, and 19. In some examples, itmay be desirable to place the heat exchanger 40 on a roof of a building.

In other examples, the heat exchanger 40 can be a liquid-to-liquid heatexchanger and can be connected to an external cooling fluid (such aschilled water from a building supply line, as shown in FIG. 20). Morespecifically, the heat exchanger 40 can be connected to a chilled watersupply line of a building, thereby allowing heat rejected from thecooling apparatus 1 to be removed from the room 425 where the coolingapparatus 1 is installed and transferred to the chilled water lineinstead of being rejected to the room air, where it would otherwiseresult in an increase in the room air temperature. In other examples,the liquid-to-liquid heat exchanger 40 can be connected to a glycol loopcirculating to a dry cooler or chiller located outside of or on top ofthe building. In one example, the heat exchanger 40 can be a StandardXchange Brazepak brazed plate heat exchanger from Xylem, Inc. of RyeBrook, N.Y.

The flow rate of coolant 50 through the heat exchanger 40 can bemonitored and controlled to avoid reducing the temperature of thelow-temperature 53 coolant to or below the dew point of ambient air inthe room 425 where the surface to be cooled 12 is located. Reaching ordropping below the dew point of the ambient air is undesirable, since itcan cause condensation to form on an outer surface of the flexibletubing 225 or other components of the cooling apparatus 1. If thisoccurs, water droplets can form on and fall from the outer surface ofthe tubing 225 onto sensitive electrical components within the server400, such as the microprocessor 415 or memory modules 420, which isundesirable. Consequently, the low-temperature 53 coolant should bemaintained at a temperature above the dew point of ambient air in theroom 425 to ensure that condensation will not form on any components ofthe cooling apparatus 1 that are in close proximity to sensitiveelectrical devices being cooled.

In some examples, if the low-temperature 53 coolant is cooled below thedew point of ambient air in the room by the heat exchanger 40, apreheater can be provided in line with, or upstream of, the line (e.g.flexible tubing 225) that transports coolant 50 flow into the server 400housing and into the heat sink module 100. The preheater can be used toheat the coolant flow to bring the coolant temperature above its dewpoint temperature, thereby avoiding potential complications caused bycondensation forming on the lines within the server housing. In someexamples, the preheater can be configured to operate only when needed,such as when the temperature of the low-temperature coolant drops belowits dew point.

The temperature of the low-temperature coolant 52 can be monitored withone or more temperature sensors positioned in the cooling lines, anddata from the sensors can be input to the controller. For instance, afirst temperature sensor can be positioned upstream of the preheater,and a second temperature sensor can be positioned downstream of thepreheater. When the first temperature sensor detects a coolanttemperature that is below the dew point of ambient air in the room 425,the controller can be configured to activate the preheater to heat thelow-temperature coolant 52 to bring the temperature of thelow-temperature coolant above the dew point of the ambient air in theroom 425. In some examples, the rate of heat addition can be ramped upgradually, and once the temperature detected by the second temperaturesensor is above the dew point of the ambient air, the controller can beconfigured to stop ramping the rate of heat addition and instead holdthe heat addition constant. The controller can continue instructing thepreheater to heat the low-temperature coolant 52 until preheating is nolonger needed. For instance, the controller can continue instructing thepreheater to heat the low-temperature coolant 52 until the temperaturedetected by the first temperature sensor is above the dew point of theambient air.

Although the preheating process described above includes measuring thetemperature of the low-temperature coolant 52 directly, in otherexamples the surface temperature of the outer surface of the tubing(e.g. 225) can be measured instead of measuring the coolant temperaturedirectly. For instance, temperature sensors can be affixed directly tothe outer surface of the tubing (e.g. 225) upstream and downstream ofthe preheater. In some instances, this approach can permit fasterinstallation of the temperature sensors and can reduce the number ofpotential leak points in the cooling apparatus 1. In other examples, acontactless temperature-sensing device, such as an infrared temperaturesensor, can be used to detect the temperature of the coolant or thetemperature of the tubing 225 transporting the coolant.

To ensure the temperature of the low temperature coolant 52 remainsabove the dew point temperature of the ambient air, the flow ratethrough the heat exchanger 40 can be decreased and/or the fan speed of afan 26 mounted on the heat exchanger 40 can be reduced to lower the heatrejection rate from the heat exchanger 40 if a low temperature thresholdis detected in the low-temperature coolant. This step can be takeninstead of, or in conjunction with, using the preheater to avoid dewformation on any components of the cooling apparatus 1.

Electronic Control System

The cooling apparatus 1 can include an electronic control system 850, asshown in FIG. 12Q, to enhance performance and reduce power consumptionof the cooling apparatus 1. In some examples, the electronic controlsystem 850 can include a microcontroller. The microcontroller can beelectrically connected to one or more system components, such as a heatexchanger fan 26, a pressure regulator 60, a shut-off valve, or a pump20, and can be configured to dynamically adjust settings of the one ormore components within the cooling apparatus 1 during operation of thecooing apparatus to enhance performance and/or reduce overall powerconsumption. In one example, the microcontroller can be electricallyconnected to a variable speed drive for the pump 20, as described inU.S. Patent Publication No. 2006/0196627 to Shedd et al., which ishereby incorporated by reference in its entirety. The microcontrollerand the variable speed drive can allow the pump 20 to operate at a lowerpower when the thermal load decreases. For instance, the operatingpressure at the pump outlet 22 can be decreased when the thermal loadfalls, thereby decreasing the flow rate through the cooling apparatus 1and the heat sink modules 100 fluidly connected thereto. The ability tooperate the variable speed drive at a lower power conserves energy, andis therefore desirable. Where the cooling apparatus 1 includesindependent redundant cooling loops, the electronic control system 850can be configured to operate a first cooling loop while a second coolingloop is on standby. In some examples, the electronic control system 850can be configured to activate the second cooling loop only if the firstcooling loop experiences a malfunction or is otherwise unable toeffectively cool the surface to be cooled 12. In this way, the redundantcooling apparatus 1 can reduce power consumption by about 50% comparedto a redundant cooling apparatus where both cooling loops operatecontinuously.

When a redundant cooling apparatus is provided, the apparatus may runfor long periods of time (e.g. years) without experiencing anymalfunctions or component failures. Consequently, during these longperiods of time, only one cooling loop will be needed and the othercooling loop will remain on standby. To ensure that each cooling loopremains functional and ready to operate when needed, the electroniccontrol system 850 can alternate between operating the first coolingloop and the second cooling loop when only one cooling loop is needed.For instance, the control system can be configured to activate the firstcooling loop for a certain period of time (e.g. a number of hours ordays) while the second cooling loop remains on standby. Once the certainperiod of time has passed, the electronic control system 850 can thenactivate the second cooling loop, and once the second cooling loop isoperating as desired, can place the first cooling loop on standby.Cycling between operating the first cooling loop and operating thesecond cooling loop can extend the life of certain system componentswithin each loop (e.g. pump seals) and can increase the likelihood thatthe standby loop is ready for operation if the other cooling loopexperiences a malfunction. Cycling between the first and second coolingloops can also ensure that operating time is equally distributed betweenthe two cooling loops, thereby potentially increasing the overall usefullife of the redundant cooling apparatus 1.

The cooling apparatus 1 can include one or more sensors that deliverdata to the electronic control system 850 to allow a malfunction withinthe cooling apparatus 1 to be detected and communicated to an operator.The cooling apparatus can include one or more temperature sensors,pressure sensors, visual flow sensors, flow quality sensors, vibrationsensors, smoke detectors, fluorocarbon detectors, or leak detectors thatdeliver data to the electronic control system 850. Each sensor can beelectrically connected or wirelessly connected to the electronic controlsystem 850. Upon detection of a malfunction within the cooling apparatus1, the electronic control system 850 can be configured to notify asystem operator, for example, with a visual or audible alarm. Theelectronic control system 850 can be configured to send an electronicmessage (e.g. an email or text message) to a system operator to alertthe operator of the malfunction. The electronic message can includespecific details associated with the malfunction, including datarecorded from the one or more sensors connected to the electroniccontrol system 850. The electronic message can also include a partnumber associated with the component that has likely failed to permitthe operator to immediately determine if the part exists in localinventory, and if not, to order a replacement part from a vendor as soonas possible. The electronic message, and any data relating to themalfunction, can be stored in a computer readable medium and/ortransmitted to the system manufacturer for quality control, warranty,and/or recall purposes.

Cooling Apparatus with Rooftop Dry Cooler

FIG. 12P shows a schematic of a cooling apparatus 1 having a primarycooling loop 300, a first bypass 305, and a second bypass 310, where thefirst bypass 305 is connected to a heat exchanger 40 that can be arooftop dry cooler. The cooling apparatus 1 can include an electroniccontrol system 850 having a microcontroller that receives inputs fromsensors regarding flow rate, pressure, and temperature and determinesheat removed (W), rate of heat removed (kW-h over time), and pump 20power consumption. The cooling apparatus 1 can include two pumps 20arranged in a parallel configuration for redundancy. Shut-off valves 250can be provided near each pump inlet 21 and outlet 22, thereby allowingfor hot-swapping of a failed pump 20. The shut-off valves 250 can beelectronically controlled by the electronic control system 850 ormanually controlled, depending on the complexity of the coolingapparatus 1. Where the shut-off valves 250 are electronicallycontrolled, a motor fail-safe 855 (see, e.g. FIG. 12P) can be providedto monitor the status of the pumps 20, and in case of pump failure, candeactivate the failed pump and activate the non-failed pump to ensurecontinued flow of coolant through the primary cooling loop 300 to thesurface to be cooled 12. In some examples, the cooling apparatus 1 caninclude a strainer 260 downstream of the pumps 20 and a filter 260upstream of the pumps 20. In some examples, the pressure regulator 60located between the heat exchanger 40 and the reservoir 200 can be aback-pressure valve, such as a liquid relief valve manufactured byKunkle Valve and available from Pentair, Ltd. of Minneapolis, Minn. Insome examples, the pressure regulator 60 positioned in the first bypass305 can be a back pressure valve, such as a liquid relief valvemanufactured by Cash Valve, also available from Pentair, Ltd.

Portable Cooling Device

FIG. 74 shows a portable cooling device 750 that includes a plurality ofheat sink modules 100 mounted on a portable layer 755. In some examples,the portable layer 755 can be a rigid material, such as metal, carbonfiber composite, or plastic. In other examples, the portable layer 755can be a conformable material, such as fabric, foam, or an insulatingblanket. The portable layer 755 can be contoured to correspond to anyheated surface 12. The plurality of heat sink modules (100, 700) can beattached to the portable layer 755 by any suitable method of adhesion.The heat sink modules (100, 700) can be fluidly connected in seriesand/or parallel configurations. The portable cooling device 750 caninclude one or more inlet connections 236 and one or more outletconnections 237 that can be connected to a cooling apparatus 1 thatdelivers a flow of pressurized coolant 50 to the portable cooling device750 to permit cooling of the heated surface 12 through sensible andlatent heating of the coolant within the plurality of heat sink modules.In some examples, each heat sink module can be mounted on a thermallyconductive base member 430. Where the portable layer 755 is made from aninsulated blanket or other insulating member, the portable coolingdevice 750 can be wrapped around a vessel to cool the vessel and itscontents. In this example, the portable layer 755 can include suitablefastening devices (e.g. snaps, ties, zippers, Velcro, or magnets) toallow the portable cooling device to be removably attached to thevessel.

Heat Pipe

In some examples, a heat pipe can be used as the thermally conductivebase member 430. The heat pipe can include a sealed casing and a wick, avapor cavity, and a working fluid within the sealed casing. In someexamples, the working fluid can be R134a. During a thermal cycle of theheat pipe, the working fluid evaporates to vapor as it absorbs thermalenergy (e.g. from a microprocessor 415 in a server 400). The vapor thenmigrates along the vapor cavity from a first end of the heat pipe towarda second end of the heat pipe, where the second end is at a lowertemperature than the first end. As the vapor migrates toward the secondend of the heat pipe, it cools and condenses back to fluid, which isabsorbed by the wick. The fluid in the wick then flows back to the firstend of the heat pipe due to gravity or capillary action. The thermalcycle then repeats itself.

In some cooling applications, size, shape, or environmental constraintsmay prevent a heat sink module 100 from being placed directly on acomponent or device that requires cooling. In these examples, a heatpipe can be used to transfer heat from the component or device to theheat sink module 100 located at a distance from the component or device.For instance, a first portion of the heat pipe can be placed in thermalcommunication with a heat-providing surface, and a second portion of theheat pipe can be placed in thermal communication with the heat sinkmodule 100. This approach can allow the heat sink module 100 toefficiently absorb heat from the heat-providing surface without being indirect contact or near to the heat-providing surface.

The heat pipe can be any suitable heat pipe, such as a heat pipeavailable from Advanced Cooling Technologies, Inc. located in Lancaster,Pa.

Heat Sink Module Examples

In one example, a heat sink module 100 for cooling a heat providingsurface 12 can include an inlet chamber formed 145 within the heat sinkmodule and an outlet chamber 150 formed within the heat sink module. Theoutlet chamber 150 can have an open portion, such as an open surface.The open portion can be enclosed by the heat providing surface 12 toform a sealed chamber when the heat sink module 100 is installed on theheat providing surface 12, as shown in FIG. 26. The heat sink module 100can include a dividing member 195 disposed between the inlet chamber 145and the outlet chamber 150. The dividing member 195 can include a firstplurality of orifices 155 formed in the dividing member. The firstplurality of orifices 155 can extend from a top surface of the dividingmember 195 to a bottom surface of the dividing member 195. The firstplurality of orifices 155 can be configured to deliver a plurality ofjet streams 16 of coolant 50 into the outlet chamber 150 and against theheat-providing surface 12 when the heat sink module 100 is installed onthe heat providing surface 12 and when pressurized coolant 50 isdelivered to the inlet chamber 145.

A distance between the bottom surface of the dividing member 195 and theheat providing surface 12 can define a jet height 18 of the plurality oforifices 155 when the heat sink module 100 is installed on the heatproviding surface 12. The jet height 18 can be about 0.01-0.75,0.05-0.5, 0.05-0.25, 0.020-0.25, 0.03-0.125, or 0.04-0.08 in.

The first plurality of orifices 155 can have an average diameter ofabout 0.001-0.020, 0.001-0.2, 0.001-0.150, 0.001-0.120, 0.001-0.005, or0.030-0.050 in. The first plurality of orifices 155 can have an averagediameter of D and an average length of L, and L divided by D can begreater than or equal to one or about 1-10, 1-8, 1-6, 1-4, or 1-3.

The dividing member can have a thickness of about 0.005-0.25, 0.020-0.1,0.025-0.08, 0.025-0.075, 0.040-0.070, 0.1-0.25, or 0.040-0.070 in. Eachorifice of the first plurality of orifices 155 can have a central axis,and the central axes of the first plurality of orifices 155 can bearranged at an angle of about 20-80, 30-60, 40-50, or 45 degrees withrespect to the surface to be cooled 12.

The first plurality of orifices 155 can be arranged in an array 76, andthe array can be organized into staggered columns 77 and staggered rows78, as shown in FIG. 31, such that a given orifice 155 in a given column77 and a given row 78 does not have a corresponding orifice 155 in aneighboring row 78 in the given column 77 or a corresponding orifice ina neighboring column 77 in the given row 78.

The heat sink module 100 can include a second plurality of orifices 156extending from the inlet chamber 145 to a rear wall of the outletchamber 150, as shown in FIG. 38. The second plurality of orifices 156can be configured to deliver a plurality of anti-pooling jet streams ofcoolant 16 to a rear portion of the outlet chamber 150 when pressurizedcoolant is provided to the inlet chamber 145. Each orifice of the secondplurality of orifices comprises a central axis, wherein the central axesof the second plurality of orifices are arranged at an angle of about40-80, 50-70, or 60 degrees with respect to the surface to be cooled.The second plurality of orifices 156 can be arranged in a column alongthe rear wall of the outlet chamber 150.

The heat sink module 100 can include one or more boiling-inducingmembers 196 extending from the bottom side of the dividing member 195toward the heat providing surface, wherein the one or moreboiling-inducing members 196 are slender members extending from thebottom surface of the dividing member 195. In one example, the one ormore boiling-inducing members 196 can be configured to contact the heatproviding surface 12. In another example, the one or moreboiling-inducing members 196 can be configured to extend toward the heatproviding surface 12, but not contact the heat providing surface 12.Instead, a clearance distance can be provided between the ends of theone or more boiling-inducing members 196 and heat providing surface. Theclearance distance can be about 0.001-0.0125, 0.001-0.05, 0.001-0.02,0.001-0.01, or 0.005-0.010 in.

The inlet chamber 145 of the heat sink module 100 can decrease incross-sectional area in a direction from a front surface 175 of the heatsink module toward a rear surface 180 of the heat sink module, as shownin FIG. 26. The outlet chamber 150 of the heat sink module 100 canincrease in cross-sectional area in a direction from a front surface 170of the heat sink module toward a rear surface 180 of the heat sinkmodule.

The heat sink module 100 can include an inlet port 105 and an inletpassage 165 fluidly connecting the inlet port 105 to the inlet chamber145. The heat sink module 100 can include an outlet port 110 an outletpassage 166 fluidly connecting the outlet chamber 150 to the outlet port110. The heat sink module 100 can include a bottom surface 135 and abottom plane 19 associated with the bottom surface, as shown in FIG. 26.The inlet port 105 can have a central axis 23 that defines an angle (a)of about 10-80, 20-70, 30-60, or 40-50 degrees with respect to thebottom plane 19 of the heat sink module 100. Similarly, the outlet port110 can have a central axis that defines an angle of about 10-80, 20-70,30-60, or 40-50 degrees with respect to the bottom plane of the heatsink module.

An additive manufacturing process, such as stereolithography, can beused to manufacture the heat sink module. The stereolithography processcan include forming layers of material curable in response tosynergistic stimulation adjacent to previously formed layers of materialand successively curing the layers of material by exposing the layers ofmaterial to a pattern of synergistic stimulation corresponding tosuccessive cross-sections of the heat sink module. The material curablein response to synergistic stimulation can be a liquid photopolymer.

Method Examples

In one example, a method of cooling two heat-providing surfaces (12-1,12-2) within a server 400 using a cooling apparatus 1 having twoseries-connected heat sink modules (100-1, 100-2) can include providinga flow 51 of single-phase liquid coolant 50 to an inlet port 105-1 of afirst heat sink module 100-1 mounted on a first heat-providing surface12-1 within a server 400. A first amount of heat can be transferred fromthe first heat-providing surface 12-1 to the single-phase liquid coolant50 resulting in vaporization of a portion of the single phase liquidcoolant 50 thereby changing the flow 51 of single-phase liquid coolant50 to two-phase bubbly flow containing liquid coolant 50 with vaporcoolant dispersed as bubbles 275 in the liquid coolant 50. The two-phasebubbly flow can have a first quality (x₁). The method can includetransporting the two-phase bubbly flow from an outlet port 110-1 of thefirst heat sink module 100-1 to an inlet port 105-1 of a second heatsink module 100-2. The second heat sink module 100-2 can be mounted on asecond heat-providing surface 12-2 within the server 400. A secondamount of heat can be transferred from the second heat-providing surface12-2 to the two-phase bubbly flow resulting in vaporization of a portionof the liquid coolant 50 within the two-phase bubbly flow therebyresulting in a change from the first quality (x₁) to a second quality(x₂). The second quality can be higher than the first quality (x₂>x₁).The energy from the first amount of heat and the second amount of heatcan be stored, at least in part, as latent heat in the two-phase bubblyflow and transported out of the server 400 through the cooling apparatus1. The amount of heat transferred out of the server 400 can be afunction of the amount of vapor formed within the two-phase bubbly flowand the heat of vaporization of the coolant.

Providing the flow 51 of single-phase liquid coolant 50 to the inletport 105-1 of the first heat sink module 100-1 can include providing aflow rate of about 0.1-10, 0.2-5, 0.3-2.5, 0.6-1.2, or 0.8-1.1 litersper minute of single-phase liquid coolant 50 to the first inlet 105-1 ofthe first heat sink module 100-1. The flow 51 of single-phase liquidcoolant 50 can be a dielectric coolant such as, for example, HFE-7000,R-245fa, HFE-7100 or a combination thereof.

Providing the flow 51 of single-phase liquid coolant 50 to the firstheat sink module 100-1 can include providing the flow 51 of single-phaseliquid coolant 50 at a predetermined temperature and a predeterminedpressure, where the predetermined temperature is slightly below thesaturation temperature (T_(sat)) of the single-phase liquid coolant 50at the predetermined pressure. The predetermined temperature can beabout 0.5-20, 0.5-15, 0.5-10, 0.5-7, 0.5-5, 0.5-3, 0.5-1, 1-20, 1-15,1-10, 1-7, 1-5, 1-3, 3-20, 3-15, 3-10, 3-7, 3-5, 5-20, 5-15, 5-10, 5-7,7-20, 7-15, 7-10, 10-20, 10-15, or 15-20 degrees C. below the saturationtemperature of the single-phase liquid coolant 50 at the predeterminedpressure.

A pressure differential of about 0.5-5.0, 0.5-3, or 1-3 psi can bemaintained between the inlet port 105-1 of the first heat sink module100-1 and the outlet port 110-1 of the first heat sink module 100-1. Thepressure differential can be suitable to promote the flow 51 to advancefrom the inlet port 105-1 of the first heat sink module 100-1 to theoutlet port 110-1 of the first heat sink module 100-1.

A saturation temperature (T_(sat), x₂) and pressure of the two-phasebubbly flow having a second quality (x₂) can be less than a saturationtemperature (T_(sat), x₁) and pressure of the two-phase flow having afirst quality (x₁) (as shown in FIG. 14B), thereby allowing the secondheat-providing surface 12-2 to be maintained at a lower temperature thanthe first heat-providing surface 12-1 when a first heat flux from thefirst heat-providing surface is approximately equal to a second heatflux from the second heat-providing surface.

The first quality (x₁) can be about 0-0.1, 0.05-0.15, 0.1-0.2,0.15-0.25, 0.2-0.3, 0.25-0.35, 0.3-0.4, 0.35-0.45, 0.4-0.5, 0.45-0.55,and the second quality (x₂) can be greater than the first quality, suchas, for example, 0-0.1, 0.05-0.15, 0.1-0.2, 0.15-0.25, 0.2-0.3,0.25-0.35, 0.3-0.4, or 0.4-0.45 greater than the first quality.

The liquid component 50 of the two-phase bubbly flow that is transportedbetween the first heat sink module 100-1 and the second heat sink module100-2 can have a temperature slightly below its saturation temperature.The pressure of the two-phase bubbly flow can be about 0.5-5.0, 0.5-3,or 1-3 psi less than the predetermined pressure of the flow 51 ofsingle-phase liquid coolant 50 provided to the inlet port 105-1 of thefirst heat sink module 100-1.

The first heat-providing surface 12-1 can be a surface of amicroprocessor 415 within the server 400. The first heat-providingsurface 12-1 can be a surface of a thermally conductive base member 430in thermal communication with a microprocessor 415 within the server400. The thermally conductive base member 430 can be a metallic baseplate mounted on the microprocessor 415 using a thermal interfacematerial.

In another example, a method of cooling two or more heat-providingsurfaces (12-1, 12-2) using a cooling apparatus 1 having two or morefluidly connected heat sink modules (e.g. 100-1, 100-2) arranged in aseries configuration can include providing a flow 51 of single-phaseliquid coolant 50 to a first inlet port 105-1 of a first heat sinkmodule 100-1 mounted on a first surface to be cooled 12-1. The flow 51of single-phase liquid coolant 50 can have a predetermined pressure anda predetermined temperature at the first inlet port 105-1 of the firstheat sink module 100-1. The predetermined temperature can be slightlybelow a saturation temperature of the coolant at the predeterminedpressure. The method can include projecting the flow 51 of single-phaseliquid coolant 50 against the first heat-providing surface 12-1 withinthe first heat sink module 100-1, where a first amount of heat istransferred from the first heat-providing surface 12-1 to the flow 51 ofsingle-phase liquid coolant 50 thereby inducing phase change in aportion of the single-phase liquid coolant 50 and thereby changing theflow 51 of single-phase liquid coolant to two-phase bubbly flowcontaining a liquid coolant 50 and a plurality of vapor bubbles 275dispersed within the liquid coolant 50. The plurality of vapor bubbles275 can have a first number density.

The method can include providing a second heat sink module 100-2 mountedon a second heat-providing surface 12-2. The second heat sink module100-2 can include a second inlet port 105-2 and a second outlet port110-2. The method can include providing a first section of tubing 225having a first end connected to the first outlet port 110-1 of the firstheat sink module 100-1 and a second end connected to the second inletport 105-2 of the second heat sink module 100-2. The first section oftubing 225 can transport the two-phase bubbly flow having the firstnumber density of vapor bubbles from the first outlet port 110-1 of thefirst heat sink module 100-1 to the second inlet port 105-2 of thesecond heat sink module 100-2. The method can include projecting thetwo-phase bubbly flow having the first number density against the secondheat-providing surface 12-2 within the second heat sink module 100-2,where a second amount of heat is transferred from the secondheat-providing surface 12-2 to the two-phase bubbly flow having a firstnumber density and thereby changing two-phase bubbly flow having a firstnumber density to a two-phase bubbly flow having a second number densitygreater than the first number density.

A saturation temperature and pressure of the two-phase flow having asecond number density can be less than a saturation temperature andpressure of the two-phase flow having a first number density, therebyallowing the second heat-providing surface 12-2 to be maintained at alower temperature than the first heat-providing surface 12-1 when afirst heat flux from the first heat-providing surface is approximatelyequal to a second heat flux from the second heat-providing surface.

The predetermined temperature of the flow 51 of single-phase liquidcoolant 50 at the first inlet port 105-1 of the first heat sink module100-1 can be about 0.5-20, 0.5-15, 0.5-10, 0.5-7, 0.5-5, 0.5-3, 0.5-1,1-20, 1-15, 1-10, 1-7, 1-5, 1-3, 3-20, 3-15, 3-10, 3-7, 3-5, 5-20, 5-15,5-10, 5-7, 7-20, 7-15, 7-10, 10-20, 10-15, or 15-20 degrees C. below thesaturation temperature of the flow 51 of single-phase liquid coolant 50at the predetermined pressure of the flow 51 of single-phase liquidcoolant at the first inlet of the first heat sink module.

Providing the flow 51 of single-phase liquid coolant 50 to the inletport 105-1 of the first heat sink module 100-1 can include providing aflow rate of about 0.1-10, 0.2-5, 0.3-2.5, 0.6-1.2, or 0.8-1.1 litersper minute of single-phase liquid coolant 50 to the first inlet port100-1 of the first heat sink module 100-1.

The liquid in the two-phase bubbly flow being transported between thefirst heat sink module 100-1 and the second heat sink module 100-2 canhave a temperature at or slightly below its saturation temperature,where a pressure of the two-phase bubbly flow having a first numberdensity is about 0.5-5.0, 0.5-3, or 1-3 psi less than the predeterminedpressure of the flow 51 of single-phase liquid coolant 50 provided tothe first heat sink module 100-1.

The first heat sink module 100-1 can include an inlet chamber 145 formedwithin the first heat sink module and an outlet chamber 150 formedwithin the first heat sink module. The outlet chamber 150 can have anopen portion enclosed by the first surface to be cooled 12-1 when thefirst heat sink module 100-1 is mounted on the first surface to becooled 12-1. The first heat sink module 100-1 can include a plurality oforifices 155 extending from the inlet chamber 145 to the outlet chamber150. Projecting the flow 51 of single-phase liquid coolant 50 againstthe first heat-providing surface 12-1 can include projecting a pluralityof jet streams 16 of single-phase liquid coolant 50 through theplurality of orifices 155 into the outlet chamber 150 and against thefirst surface to be cooled 12-1 when the flow 51 of single-phase liquidcoolant 50 is provided to the inlet chamber 145 from the first inletport 105-1 of the first heat sink module 100-1. The first plurality oforifices 155 can have an average diameter of about 0.001-0.020,0.001-0.2, 0.001-0.150, 0.001-0.120, 0.001-0.005, or 0.030-0.050 inches.Outlets of the plurality of orifices 155 can be arranged at a jet height18 from the first surface to be cooled 12-1. The jet height 18 can beabout 0.01-0.75, 0.05-0.5, 0.05-0.25, 0.020-0.25, 0.03-0.125, or0.04-0.08 inches. At least one of the orifices 155 can have a centralaxis 74 arranged at an angle of about 30-60, 40-50, or 45 degrees withrespect to the first surface to be cooled 12-1.

In another example, a method of cooling two microprocessors 415 on amotherboard 405 using a two-phase cooling apparatus 1 having twoseries-connected heat sink modules (100-1, 100-2) can include providinga flow 51 of single-phase liquid coolant 50 to an inlet port 105 of afirst heat sink module 100-1 mounted on a first thermally conductivebase member 430. The first thermally conductive base member 430 can bemounted on a first microprocessor 415 mounted on a motherboard 405,where heat is transferred from the first microprocessor 415 through thefirst thermally conductive base member 430 and to the flow 51 ofsingle-phase liquid coolant 50 resulting in boiling of a first portionof the single-phase liquid coolant 50, thereby changing the flow 51 ofsingle-phase liquid coolant 50 to two-phase bubbly flow having a firstquality (x₁). The method can include transporting the two-phase bubblyflow from an outlet port 110 of the first heat sink module 100-1 to aninlet port 105 of a second heat sink module 100-2 through flexibletubing 225. The second heat sink module 100-2 can be mounted on a secondthermally conductive base member 430 that is mounted on a secondmicroprocessor 415 mounted on the motherboard 405. Heat can betransferred from the second microprocessor 415 through the secondthermally conductive base member 430 and to the two-phase bubbly flowresulting in vaporization of a portion of liquid coolant 50 within thetwo-phase bubbly flow thereby resulting in a change from the firstquality (x₁) to a second quality (x₁), the second quality being higherthan the first quality (i.e. x₂>x₁).

The elements and method steps described herein can be used in anycombination whether explicitly described or not. All combinations ofmethod steps as described herein can be performed in any order, unlessotherwise specified or clearly implied to the contrary by the context inwhich the referenced combination is made.

As used herein, the singular forms “a,” “an,” and “the” include pluralreferents unless the content clearly dictates otherwise.

Numerical ranges as used herein are intended to include every number andsubset of numbers contained within that range, whether specificallydisclosed or not. Further, these numerical ranges should be construed asproviding support for a claim directed to any number or subset ofnumbers in that range. For example, a disclosure of from 1 to 10 shouldbe construed as supporting a range of from 2 to 8, from 3 to 7, from 5to 6, from 1 to 9, from 3.6 to 4.6, from 3.5 to 9.9, and so forth.

All patents, patent publications, and peer-reviewed publications (i.e.,“references”) cited herein are expressly incorporated by reference tothe same extent as if each individual reference were specifically andindividually indicated as being incorporated by reference. In case ofconflict between the present disclosure and the incorporated references,the present disclosure controls.

The methods and compositions of the present invention can comprise,consist of, or consist essentially of the essential elements andlimitations described herein, as well as any additional or optionalsteps, components, or limitations described herein or otherwise usefulin the art.

It is understood that the invention is not confined to the particularconstruction and arrangement of parts herein illustrated and described,but embraces such modified forms thereof as come within the scope of theclaims.

Several impingement technologies exist, but few have shown commercialpromise and none have gained wide-scale commercial acceptance to datedue to instability issues, relatively high flow rate requirements,limitations on scalability, and other shortcomings.

An improved heat sink module 100 with an array of impinging jet streams16 has been developed and is described herein. By providing modular heatsink modules 100 that can be connected in series and parallelconfigurations to cool a plurality of surfaces 12 simultaneously,selecting an appropriate jet height 18, selecting an appropriate coolantpressure and temperature, selecting an appropriate dielectric coolant50, selecting an appropriate bypass flow configuration, and angling theorifices 155 at a non-perpendicular angle with respect to the surface tobe cooled 12, a scalable jet impingement technology has been developed100. Importantly, the heat sink modules 100 described herein are compactand easy to package inside new and existing server 400 and personalcomputer housings, as well as for use on other electrical and mechanicaldevices and chemical processing equipment.

The foregoing description has been presented for purposes ofillustration and description. It is not intended to be exhaustive or tolimit the claims to the embodiments disclosed. Other modifications andvariations may be possible in view of the above teachings. Theembodiments were chosen and described to explain the principles of theinvention and its practical application to enable others skilled in theart to best utilize the invention in various embodiments and variousmodifications as are suited to the particular use contemplated. It isintended that the claims be construed to include other alternativeembodiments of the invention except insofar as limited by the prior art.

What is claimed is:
 1. A method of cooling two heat-providing surfaceswithin a server using a cooling apparatus comprising twoseries-connected heat sink modules, the method comprising: providing aflow of single-phase liquid coolant to an inlet port of a first heatsink module mounted on a first heat-providing surface within a server,wherein a first amount of heat is transferred from the firstheat-providing surface to the single-phase liquid coolant resulting invaporization of a portion of the single-phase liquid coolant therebychanging the flow of single-phase liquid coolant to two-phase bubblyflow comprising liquid coolant with vapor coolant dispersed as bubblesin the liquid coolant, the two-phase bubbly flow having a first quality;and transporting the two-phase bubbly flow from an outlet port of thefirst heat sink module to an inlet port of a second heat sink module,wherein the second heat sink module is mounted on a secondheat-providing surface within the server, wherein a second amount ofheat is transferred from the second heat-providing surface to thetwo-phase bubbly flow resulting in vaporization of a portion of theliquid coolant within the two-phase bubbly flow thereby resulting in achange from the first quality to a second quality, the second qualitybeing higher than the first quality, wherein energy from the firstamount of heat and the second amount of heat are stored, at least inpart, as latent heat in the two-phase bubbly flow and transported out ofthe server through the cooling apparatus.
 2. The method of claim 1,wherein a saturation temperature and pressure of the two-phase flowhaving a second quality is less than a saturation temperature andpressure of the two-phase flow having a first quality, thereby allowingthe second heat-providing surface to be maintained at a lowertemperature than the first heat-providing surface when a first heat fluxfrom the first heat-providing surface is approximately equal to a secondheat flux from the second heat-providing surface.
 3. The method of claim1, wherein providing the flow of single-phase liquid coolant to theinlet port of the first heat sink module comprises providing a flow rateof about 0.1-10, 0.2-5, 0.3-2.5, 0.6-1.2, or 0.8-1.1 liters per minuteof single-phase liquid coolant to the first inlet of the first heat sinkmodule.
 4. The method of claim 1, wherein the flow of single-phaseliquid coolant comprises a dielectric coolant.
 5. The method of claim 4,wherein the dielectric coolant is HFE-7000, R-245fa, or a combinationthereof.
 6. The method of claim 1, wherein providing the flow ofsingle-phase liquid coolant to the first heat sink module comprisesproviding the flow of single-phase liquid coolant at a predeterminedtemperature and a predetermined pressure, wherein the predeterminedtemperature is slightly below the saturation temperature of the flow ofsingle-phase liquid coolant at the predetermined pressure.
 7. The methodof claim 6, wherein the predetermined temperature is about 0.5-20,0.5-15, 0.5-10, 0.5-7, 0.5-5, 0.5-3, 0.5-1, 1-20, 1-15, 1-10, 1-7, 1-5,1-3, 3-20, 3-15, 3-10, 3-7, 3-5, 5-20, 5-15, 5-10, 5-7, 7-20, 7-15,7-10, 10-20, 10-15, or 15-20 degrees C. below the saturation temperatureof the flow of single-phase liquid coolant at the predeterminedpressure.
 8. The method of claim 1, further comprising providing apressure differential of about 0.5-5.0, 0.5-3, or 1-3 psi between theinlet port of the first heat sink module and the outlet port of thefirst heat sink module, wherein the pressure differential is suitable topromote the flow to advance from the inlet port of the first heat sinkmodule to the outlet port of the first heat sink module.
 9. The methodof claim 1, wherein the liquid coolant in the two-phase bubbly flow thatis transported between the first heat sink module and the second heatsink module has a temperature at or slightly below its saturationtemperature, the pressure of the two-phase bubbly flow being about0.5-5.0, 0.5-3, or 1-3 psi less than the predetermined pressure of theflow of single-phase liquid coolant provided to the inlet port of thefirst heat sink module.
 10. The method of claim 1, wherein the firstquality is 0-0.1, 0.05-0.15, 0.1-0.2, 0.15-0.25, 0.2-0.3, 0.25-0.35,0.3-0.4, 0.35-0.45, 0.4-0.5, 0.45-0.55, and the second quality is 0-0.1,0.05-0.15, 0.1-0.2, 0.15-0.25, 0.2-0.3, 0.25-0.35, 0.3-0.4, or 0.4-0.45greater than the first quality.
 11. The method of claim 1, wherein thefirst heat-providing surface comprises a surface of a thermallyconductive base member in thermal communication with a microprocessorwithin the server.
 12. A method of cooling two or more heat-providingsurfaces using a cooling apparatus comprising two or more fluidlyconnected heat sink modules arranged in a series configuration, themethod comprising: providing a flow of single-phase liquid coolant to afirst inlet port of a first heat sink module mounted on a firstheat-providing surface, the single-phase liquid coolant having apredetermined pressure and a predetermined temperature at the firstinlet port of the first heat sink module, the predetermined temperaturebeing slightly below a saturation temperature of the single-phase liquidcoolant at the predetermined pressure; projecting the flow ofsingle-phase liquid coolant against the first heat-providing surfacewithin the first heat sink module, wherein a first amount of heat istransferred from the first heat-providing surface to the flow ofsingle-phase liquid coolant thereby inducing phase change in a portionof the flow of single-phase liquid coolant and thereby changing the flowof single-phase liquid coolant to two-phase bubbly flow comprising aliquid coolant and a plurality of vapor bubbles dispersed within theliquid coolant, the plurality of vapor bubbles having a first numberdensity; providing a second heat sink module mounted on a secondheat-providing surface, the second heat sink module comprising a secondinlet port and a second outlet port; and providing a first section oftubing having a first end connected to the first outlet port of thefirst heat sink module and a second end connected to the second inletport of the second heat sink module, wherein the first section of tubingtransports the two-phase bubbly flow having the first number densityfrom the first outlet port of the first heat sink module to the secondinlet port of the second heat sink module; and projecting the two-phasebubbly flow having the first number density against the secondheat-providing surface within the second heat sink module, wherein asecond amount of heat is transferred from the second heat-providingsurface to the two-phase bubbly flow having a first number density andthereby changing two-phase bubbly flow having a first number density toa two-phase bubbly flow having a second number density greater than thefirst number density.
 13. The method of claim 1, wherein a saturationtemperature and pressure of the two-phase flow having a second numberdensity is less than a saturation temperature and pressure of thetwo-phase flow having a first number density, thereby allowing thesecond heat-providing surface to be maintained at a lower temperaturethan the first heat-providing surface when a first heat flux from thefirst heat-providing surface is approximately equal to a second heatflux from the second heat-providing surface.
 14. The method of claim 12,wherein the predetermined temperature of the flow of single-phase liquidcoolant at the first inlet port of the first heat sink module is about0.5-20, 0.5-15, 0.5-10, 0.5-7, 0.5-5, 0.5-3, 0.5-1, 1-20, 1-15, 1-10,1-7, 1-5, 1-3, 3-20, 3-15, 3-10, 3-7, 3-5, 5-20, 5-15, 5-10, 5-7, 7-20,7-15, 7-10, 10-20, 10-15, or 15-20 degrees C. below the saturationtemperature of the flow of single-phase liquid coolant at thepredetermined pressure of the flow of single-phase liquid coolant at thefirst inlet of the first heat sink module.
 15. The method of claim 12,wherein providing the flow of single-phase liquid coolant to the inletport of the first heat sink module comprises providing a flow rate ofabout 0.1-10, 0.2-5, 0.3-2.5, 0.6-1.2, or 0.8-1.1 liters per minute ofsingle-phase liquid coolant to the first inlet port of the first heatsink module.
 16. The method of claim 12, wherein the liquid in thetwo-phase bubbly flow being transported between the first heat sinkmodule and the second heat sink module has a temperature at or slightlybelow its saturation temperature, wherein a pressure of the two-phasebubbly flow having a first number density is about 0.5-5.0, 0.5-3, or1-3 psi less than the predetermined pressure of the flow of single-phaseliquid coolant provided to the first heat sink module.
 17. The method ofclaim 12, wherein the first heat sink module comprises: an inlet chamberformed within the first heat sink module; an outlet chamber formedwithin the first heat sink module, the outlet chamber having an openportion, the open portion configured to be enclosed by the firstheat-providing surface when the first heat sink module is mounted on thefirst heat-providing surface; and a plurality of orifices extending fromthe inlet chamber to the outlet chamber, wherein projecting the flow ofsingle-phase liquid coolant against the first heat-providing surfacewithin the first heat sink module comprises projecting a plurality ofjet streams of single-phase liquid coolant into the outlet chamber andagainst the first heat-providing surface when the flow of single-phaseliquid coolant is provided to the inlet chamber from the first inletport of the first heat sink module.
 18. The method of claim 17, whereinthe first plurality of orifices have an average diameter of about0.001-0.020, 0.001-0.2, 0.001-0.150, 0.001-0.120, 0.001-0.005, or0.030-0.050 inches and are arranged at a jet height from the firstheat-providing surface, the jet height being about 0.01-0.75, 0.05-0.5,0.05-0.25, 0.020-0.25, 0.03-0.125, or 0.04-0.08 inches.
 19. The methodof claim 17, wherein at least one orifice of the plurality of orificescomprises a central axis, the central axis being arranged at an angle ofabout 30-60, 40-50, or 45 degrees with respect to the firstheat-providing surface.
 20. A method of cooling two microprocessors on amotherboard using a two-phase cooling apparatus comprising twoseries-connected heat sink modules, the method comprising: providing aflow of single-phase liquid coolant to an inlet port of a first heatsink module mounted on a first thermally conductive base member, thefirst thermally conductive base member being mounted on a firstmicroprocessor on a motherboard, wherein heat is transferred from thefirst microprocessor through the first thermally conductive base memberand to the flow of single-phase liquid coolant resulting in boiling of afirst portion of the single-phase liquid coolant thereby changing theflow of single-phase liquid coolant to two-phase bubbly flow having afirst quality; and transporting the two-phase bubbly flow from an outletport of the first heat sink module to an inlet port of a second heatsink module through flexible tubing, wherein the second heat sink moduleis mounted on a second thermally conductive base member, the secondthermally conductive base member being mounted on a secondmicroprocessor on the motherboard, wherein heat is transferred from thesecond microprocessor through the second thermally conductive basemember and to the two-phase bubbly flow resulting in vaporization of aportion of liquid coolant within the two-phase bubbly flow therebyresulting in a change from the first quality to a second quality, thesecond quality being higher than the first quality.